Merge pull request #13 from kyuno053/feat/user-preferences-sidebar-nav

Préférences utilisateur (thème) + sidebar avec icônes et repli

apps/api/features/preferences.feature

@@ -0,0 +1,23 @@
+Feature: User preferences (theme)
+  As a signed-in user
+  I want to choose a light, dark, or system theme
+  So that the app matches how I like to read it
+
+  Scenario: A visitor without a session cannot read preferences
+    When I send a GET request to "/preferences"
+    Then the response status should be 401
+    And the response error code should be "NOT_AUTHENTICATED"
+
+  Scenario: A signed-in user with no preferences yet defaults to SYSTEM
+    Given a profile already exists with email "alice@example.com" and password "correct-horse-battery-staple"
+    And I log in with email "alice@example.com" and password "correct-horse-battery-staple"
+    When I request my preferences
+    Then the response status should be 200
+    And my theme preference should be "SYSTEM"
+
+  Scenario: A signed-in user sets their theme preference
+    Given a profile already exists with email "alice@example.com" and password "correct-horse-battery-staple"
+    And I log in with email "alice@example.com" and password "correct-horse-battery-staple"
+    When I set my theme preference to "DARK"
+    Then the response status should be 200
+    And my theme preference should be "DARK"

apps/api/features/step-definitions/preferences.steps.ts

@@ -0,0 +1,15 @@
+import assert from "node:assert/strict";
+import { Then, When } from "@cucumber/cucumber";
+import type { CustomWorld } from "../support/world.js";
+
+When("I request my preferences", async function (this: CustomWorld) {
+  this.response = await this.agent.get("/preferences");
+});
+
+When("I set my theme preference to {string}", async function (this: CustomWorld, theme: string) {
+  this.response = await this.agent.patch("/preferences").send({ theme });
+});
+
+Then("my theme preference should be {string}", function (this: CustomWorld, theme: string) {
+  assert.equal(this.response.body.theme, theme);
+});

apps/api/prisma/migrations/20260817120000_add_user_preference/migration.sql

@@ -0,0 +1,13 @@
+-- CreateEnum
+CREATE TYPE "ThemePreference" AS ENUM ('LIGHT', 'DARK', 'SYSTEM');
+
+-- CreateTable
+CREATE TABLE "user_preference" (
+    "user_profile_id" INTEGER NOT NULL,
+    "theme" "ThemePreference" NOT NULL DEFAULT 'SYSTEM',
+
+    CONSTRAINT "user_preference_pkey" PRIMARY KEY ("user_profile_id")
+);
+
+-- AddForeignKey
+ALTER TABLE "user_preference" ADD CONSTRAINT "user_preference_user_profile_id_fkey" FOREIGN KEY ("user_profile_id") REFERENCES "user_profiles"("id") ON DELETE CASCADE ON UPDATE CASCADE;

apps/api/prisma/schema.prisma

@@ -98,10 +98,36 @@ model UserProfile {
   /// a time — but Prisma models the admin side of a one-to-many FK as a
   /// list regardless of that real-world cardinality.
   administeredHouses House[]              @relation("HouseAdmin")
+  preferences        UserPreference?
 
   @@map("user_profiles")
 }
 
+/// Not in the original spec doc — personalization settings (theme for now,
+/// meant to grow), one row per profile, created on demand (see
+/// `preferences.service.ts`) rather than at signup — same "absent means the
+/// default" philosophy as `dietId`/allergies.
+enum ThemePreference {
+  LIGHT
+  DARK
+  /// Follow the OS/browser preference — the default. Not "no row yet" (that
+  /// case is handled in the service layer) but an explicit choice to track
+  /// the system, distinguishable from a user who hasn't decided yet if this
+  /// model ever needs that distinction.
+  SYSTEM
+}
+
+model UserPreference {
+  /// Both the primary key and the FK — a strict 1-1 with UserProfile, no
+  /// separate auto-incrementing id (a profile has at most one preferences row).
+  userProfileId Int             @id @map("user_profile_id")
+  theme         ThemePreference @default(SYSTEM)
+
+  userProfile UserProfile @relation(fields: [userProfileId], references: [id], onDelete: Cascade)
+
+  @@map("user_preference")
+}
+
 /// Explicit join table for the user_profiles <-> allergy association
 /// (documented in the spec as a plain many-to-many, no extra fields).
 model UserProfileAllergy {

apps/api/src/app.ts

@@ -6,6 +6,7 @@ import { env } from "./config/env.js";
 import { authRouter } from "./modules/auth/auth.routes.js";
 import { houseRouter } from "./modules/house/house.routes.js";
 import { planningRouter } from "./modules/planning/planning.routes.js";
+import { preferencesRouter } from "./modules/preferences/preferences.routes.js";
 import { profileRouter } from "./modules/profile/profile.routes.js";
 import { referenceRouter } from "./modules/reference/reference.routes.js";
 
@@ -28,6 +29,7 @@ export function createServer(): ExpressServer {
   server.mountRouter("/auth", authRouter);
   server.mountRouter("/house", houseRouter);
   server.mountRouter("/planning", planningRouter);
+  server.mountRouter("/preferences", preferencesRouter);
   server.mountRouter("/profile", profileRouter);
   server.mountRouter("/reference", referenceRouter);
 

apps/api/src/modules/preferences/preferences.routes.ts

@@ -0,0 +1,27 @@
+import { wrapAsyncHandler } from "@batch-cooking/express-tools";
+import { updatePreferencesSchema } from "@batch-cooking/shared";
+import { Router } from "express";
+import { type AuthLocals, requireAuth } from "../../middlewares/require-auth.js";
+import { getPreferences, updatePreferences } from "./preferences.service.js";
+
+/** Router mounted at `/preferences` in app.ts. Every route requires a session — this is the authenticated user's own preferences. */
+export const preferencesRouter = Router();
+
+preferencesRouter.get(
+  "/",
+  requireAuth,
+  wrapAsyncHandler<unknown, AuthLocals>(async (_req, res) => {
+    const preferences = await getPreferences(res.locals.userProfile.id);
+    res.status(200).json(preferences);
+  }),
+);
+
+preferencesRouter.patch(
+  "/",
+  requireAuth,
+  wrapAsyncHandler<unknown, AuthLocals>(async (req, res) => {
+    const input = updatePreferencesSchema.parse(req.body);
+    const preferences = await updatePreferences(res.locals.userProfile.id, input.theme);
+    res.status(200).json(preferences);
+  }),
+);

apps/api/src/modules/preferences/preferences.service.ts

@@ -0,0 +1,31 @@
+import type { PreferencesView, ThemePreference } from "@batch-cooking/shared";
+import { prisma } from "../../db/prisma.js";
+
+/**
+ * A profile's personalization preferences. `SYSTEM` (the schema default)
+ * is returned both when a row already says so *and* when there's no row
+ * yet at all — same "absent means the default" philosophy as
+ * `dietId`/allergies elsewhere in `profile.service.ts`, no row is created
+ * just to read it.
+ */
+export async function getPreferences(userProfileId: number): Promise<PreferencesView> {
+  const preferences = await prisma.userPreference.findUnique({ where: { userProfileId } });
+  return { theme: preferences?.theme ?? "SYSTEM" };
+}
+
+/**
+ * Sets a profile's theme preference, creating its preferences row on first
+ * write (an `upsert` rather than requiring a separate "create" step — a
+ * profile never needs to explicitly initialize this row before using it).
+ */
+export async function updatePreferences(
+  userProfileId: number,
+  theme: ThemePreference,
+): Promise<PreferencesView> {
+  const preferences = await prisma.userPreference.upsert({
+    where: { userProfileId },
+    create: { userProfileId, theme },
+    update: { theme },
+  });
+  return { theme: preferences.theme };
+}

apps/api/test-support/reset-db.ts

@@ -10,7 +10,7 @@ import { seedReferenceData } from "../src/db/reference-seed-data.js";
 export async function resetDatabase() {
   await prisma.$executeRawUnsafe(`
     TRUNCATE TABLE
-      "user_profile_allergy", "allergy", "category",
+      "user_profile_allergy", "user_preference", "allergy", "category",
       "planning_item", "planning",
       "recipe_ingredient", "step", "tech_step_mapping", "tech_step",
       "recipe", "ingredients", "sources",

apps/api/test/preferences.test.ts

@@ -0,0 +1,98 @@
+import { ErrorCode, type SignupInput } from "@batch-cooking/shared";
+import { faker } from "@faker-js/faker";
+import { expect } from "chai";
+import request from "supertest";
+import { createApp } from "../src/app.js";
+import { prisma } from "../src/db/prisma.js";
+import { resetDatabase } from "../test-support/reset-db.js";
+
+function buildSignupPayload(): SignupInput {
+  const firstName = faker.person.firstName();
+  const lastName = faker.person.lastName();
+  return {
+    firstName,
+    lastName,
+    email: faker.internet.email({ firstName, lastName }).toLowerCase(),
+    password: faker.internet.password({ length: 16 }),
+  };
+}
+
+describe("Preferences", () => {
+  const app = createApp();
+
+  beforeEach(async () => {
+    await resetDatabase();
+  });
+
+  after(async () => {
+    await prisma.$disconnect();
+  });
+
+  describe("GET /preferences", () => {
+    it("rejects requests without a session cookie with 401 NOT_AUTHENTICATED", async () => {
+      const res = await request(app).get("/preferences");
+
+      expect(res.status).to.equal(401);
+      expect(res.body.code).to.equal(ErrorCode.NOT_AUTHENTICATED);
+    });
+
+    it("defaults to SYSTEM when the profile has no preferences row yet", async () => {
+      const agent = request.agent(app);
+      await agent.post("/auth/signup").send(buildSignupPayload());
+
+      const res = await agent.get("/preferences");
+
+      expect(res.status).to.equal(200);
+      expect(res.body).to.deep.equal({ theme: "SYSTEM" });
+    });
+  });
+
+  describe("PATCH /preferences", () => {
+    it("rejects requests without a session cookie with 401 NOT_AUTHENTICATED", async () => {
+      const res = await request(app).patch("/preferences").send({ theme: "DARK" });
+
+      expect(res.status).to.equal(401);
+      expect(res.body.code).to.equal(ErrorCode.NOT_AUTHENTICATED);
+    });
+
+    it("rejects an unknown theme with 400 VALIDATION_ERROR", async () => {
+      const agent = request.agent(app);
+      await agent.post("/auth/signup").send(buildSignupPayload());
+
+      const res = await agent.patch("/preferences").send({ theme: "PURPLE" });
+
+      expect(res.status).to.equal(400);
+      expect(res.body.code).to.equal(ErrorCode.VALIDATION_ERROR);
+    });
+
+    it("creates the preferences row on first write, and reuses it on later reads/writes", async () => {
+      const agent = request.agent(app);
+      await agent.post("/auth/signup").send(buildSignupPayload());
+
+      const patchRes = await agent.patch("/preferences").send({ theme: "DARK" });
+      expect(patchRes.status).to.equal(200);
+      expect(patchRes.body).to.deep.equal({ theme: "DARK" });
+
+      const getRes = await agent.get("/preferences");
+      expect(getRes.body).to.deep.equal({ theme: "DARK" });
+
+      const secondPatchRes = await agent.patch("/preferences").send({ theme: "LIGHT" });
+      expect(secondPatchRes.body).to.deep.equal({ theme: "LIGHT" });
+
+      const secondGetRes = await agent.get("/preferences");
+      expect(secondGetRes.body).to.deep.equal({ theme: "LIGHT" });
+    });
+
+    it("scopes preferences to the caller's own profile", async () => {
+      const aliceAgent = request.agent(app);
+      await aliceAgent.post("/auth/signup").send(buildSignupPayload());
+      await aliceAgent.patch("/preferences").send({ theme: "DARK" });
+
+      const bobAgent = request.agent(app);
+      await bobAgent.post("/auth/signup").send(buildSignupPayload());
+
+      const res = await bobAgent.get("/preferences");
+      expect(res.body).to.deep.equal({ theme: "SYSTEM" });
+    });
+  });
+});

apps/web/cypress/e2e/auth.cy.ts

@@ -76,7 +76,7 @@ describe("Signup", () => {
 describe("Login", () => {
   it("logs in and lands on the home page", () => {
     cy.intercept("GET", "**/auth/me", { statusCode: 401 });
-    cy.intercept("GET", "**/planning/current", { statusCode: 200, body: null });
+    cy.intercept("GET", /\/planning\?/, { statusCode: 200, body: null });
     cy.intercept("POST", "**/auth/login", {
       statusCode: 200,
       body: {
@@ -130,7 +130,7 @@ describe("Already authenticated", () => {
         dietId: null,
       },
     });
-    cy.intercept("GET", "**/planning/current", { statusCode: 200, body: null });
+    cy.intercept("GET", /\/planning\?/, { statusCode: 200, body: null });
 
     cy.visit("/login");
     cy.url().should("not.include", "/login");
@@ -150,7 +150,7 @@ describe("Already authenticated", () => {
         dietId: null,
       },
     });
-    cy.intercept("GET", "**/planning/current", { statusCode: 200, body: null });
+    cy.intercept("GET", /\/planning\?/, { statusCode: 200, body: null });
     cy.intercept("POST", "**/auth/logout", { statusCode: 204 }).as("logout");
 
     cy.visit("/");

apps/web/cypress/e2e/onboarding.cy.ts

@@ -16,7 +16,7 @@ const signupResponse = {
 function signupAndReachOnboarding() {
   cy.intercept("GET", "**/auth/me", { statusCode: 401 });
   cy.intercept("POST", "**/auth/signup", { statusCode: 201, body: signupResponse }).as("signup");
-  cy.intercept("GET", "**/planning/current", { statusCode: 200, body: null });
+  cy.intercept("GET", /\/planning\?/, { statusCode: 200, body: null });
 
   cy.visit("/signup");
   cy.get("#firstName").type("Alice");

apps/web/cypress/e2e/sidebar.cy.ts

@@ -13,7 +13,9 @@ const authenticatedProfile = {
 describe("Sidebar — settings menu and account menu", () => {
   beforeEach(() => {
     cy.intercept("GET", "**/auth/me", { statusCode: 200, body: authenticatedProfile });
-    cy.intercept("GET", "**/planning/current", { statusCode: 200, body: null });
+    // Not "**/planning*" — that glob also matches the Vite dev request for
+    // planning-page.scss (see planning-page.cy.ts for the same gotcha).
+    cy.intercept("GET", /\/planning\?/, { statusCode: 200, body: null });
   });
 
   it("no longer lists Foyer in the main nav", () => {
@@ -21,15 +23,24 @@ describe("Sidebar — settings menu and account menu", () => {
     cy.get(".app-sidebar__nav a").should("not.contain", "Foyer");
   });
 
-  it("reveals the three settings pages behind the Paramètres toggle", () => {
+  it("reveals the four settings pages behind the Paramètres toggle", () => {
     cy.visit("/");
 
     cy.contains("a", "Compte").should("not.exist");
     cy.contains("button", "Paramètres").click();
 
     cy.contains("a", "Compte").should("have.attr", "href", "/parametres/compte");
-    cy.contains("a", "Préférences").should("have.attr", "href", "/parametres/preferences");
+    cy.contains("a", "Préférences alimentaires").should(
+      "have.attr",
+      "href",
+      "/parametres/preferences",
+    );
     cy.contains("a", "Foyer").should("have.attr", "href", "/parametres/foyer");
+    cy.contains("a", "Préférences utilisateur").should(
+      "have.attr",
+      "href",
+      "/parametres/preferences-utilisateur",
+    );
   });
 
   it("opens the account menu from the greeting and links to Mon compte", () => {
@@ -47,4 +58,26 @@ describe("Sidebar — settings menu and account menu", () => {
     cy.visit("/foyer");
     cy.url().should("include", "/parametres/foyer");
   });
+
+  it("collapses to an icon-only rail and back, persisting the choice across reloads", () => {
+    cy.visit("/");
+
+    cy.get(".app-sidebar").should("not.have.class", "collapsed");
+    cy.contains("nav a", "Planning").should("be.visible");
+
+    cy.get(".app-sidebar__collapse-toggle").click();
+    cy.get(".app-sidebar").should("have.class", "collapsed");
+    // The label text hides (not removed from the DOM — still there for the
+    // `title` tooltip/accessibility), while the link itself stays visible,
+    // icon-only.
+    cy.contains("span.label", "Planning").should("exist").and("not.be.visible");
+    cy.get("nav a[title='Planning']").should("be.visible");
+
+    cy.reload();
+    cy.get(".app-sidebar").should("have.class", "collapsed");
+
+    cy.get(".app-sidebar__collapse-toggle").click();
+    cy.get(".app-sidebar").should("not.have.class", "collapsed");
+    cy.contains("nav a", "Planning").should("be.visible");
+  });
 });

apps/web/cypress/e2e/user-preferences.cy.ts

@@ -0,0 +1,54 @@
+// Mocks the API via cy.intercept — see auth.cy.ts for the rationale.
+
+const authenticatedProfile = {
+  id: 1,
+  firstName: "Alice",
+  lastName: "Martin",
+  email: "alice@example.com",
+  tokenVersion: 0,
+  houseId: null,
+  dietId: null,
+};
+
+describe("User preferences (/parametres/preferences-utilisateur)", () => {
+  beforeEach(() => {
+    cy.intercept("GET", "**/auth/me", { statusCode: 200, body: authenticatedProfile });
+  });
+
+  it("shows SYSTEM selected by default", () => {
+    cy.intercept("GET", "**/preferences", { statusCode: 200, body: { theme: "SYSTEM" } });
+
+    cy.visit("/parametres/preferences-utilisateur");
+
+    cy.contains("label", "Système").find("input[type=radio]").should("be.checked");
+    cy.contains("label", "Clair").find("input[type=radio]").should("not.be.checked");
+    cy.contains("label", "Sombre").find("input[type=radio]").should("not.be.checked");
+    // SYSTEM never sets an override — the OS/browser preference decides.
+    cy.get("html").should("not.have.attr", "data-theme");
+  });
+
+  it("shows the previously saved theme selected, and applies it to the document", () => {
+    cy.intercept("GET", "**/preferences", { statusCode: 200, body: { theme: "DARK" } });
+
+    cy.visit("/parametres/preferences-utilisateur");
+
+    cy.contains("label", "Sombre").find("input[type=radio]").should("be.checked");
+    cy.get("html").should("have.attr", "data-theme", "dark");
+  });
+
+  it("switching theme autosaves and applies immediately, no explicit save button", () => {
+    cy.intercept("GET", "**/preferences", { statusCode: 200, body: { theme: "SYSTEM" } });
+    cy.intercept("PATCH", "**/preferences", { statusCode: 200, body: { theme: "LIGHT" } }).as(
+      "updatePreferences",
+    );
+
+    cy.visit("/parametres/preferences-utilisateur");
+    cy.contains("button", "Enregistrer").should("not.exist");
+
+    cy.contains("label", "Clair").click();
+
+    cy.wait("@updatePreferences").its("request.body").should("deep.equal", { theme: "LIGHT" });
+    cy.contains("Enregistré ✓").should("be.visible");
+    cy.get("html").should("have.attr", "data-theme", "light");
+  });
+});

apps/web/src/App.tsx

@@ -13,6 +13,7 @@ import { OnboardingHouseholdPage } from "./pages/onboarding/OnboardingHouseholdP
 import { AccountSettingsPage } from "./pages/settings/AccountSettingsPage";
 import { HouseholdSettingsPage } from "./pages/settings/HouseholdSettingsPage";
 import { PreferencesPage } from "./pages/settings/PreferencesPage";
+import { UserPreferencesPage } from "./pages/settings/UserPreferencesPage";
 
 /**
  * Top-level route table. Every authenticated section is nested under one
@@ -22,12 +23,12 @@ import { PreferencesPage } from "./pages/settings/PreferencesPage";
  * {@link RedirectIfAuthenticated}). Anything else falls back to `/`, which
  * itself redirects to `/login` if needed.
  *
- * `/parametres/*` (compte/préférences/foyer) are the settings pages,
- * reachable from the sidebar's bottom "Paramètres" menu and the account
- * menu (see `AppLayout`) — nested under `AppLayout` like every other
- * authenticated section. `/foyer` is the old, pre-split combined page's
- * path; it now just redirects to `/parametres/foyer` so an existing
- * bookmark/link keeps working.
+ * `/parametres/*` (compte/préférences alimentaires/foyer/préférences
+ * utilisateur) are the settings pages, reachable from the sidebar's bottom
+ * "Paramètres" menu and the account menu (see `AppLayout`) — nested under
+ * `AppLayout` like every other authenticated section. `/foyer` is the old,
+ * pre-split combined page's path; it now just redirects to
+ * `/parametres/foyer` so an existing bookmark/link keeps working.
  *
  * `/onboarding/*` (regime/foyer/allergens, in that order) is also
  * `RequireAuth`-gated — reached right after signup, once a session already
@@ -51,6 +52,7 @@ export function App() {
         <Route path="/parametres/compte" element={<AccountSettingsPage />} />
         <Route path="/parametres/preferences" element={<PreferencesPage />} />
         <Route path="/parametres/foyer" element={<HouseholdSettingsPage />} />
+        <Route path="/parametres/preferences-utilisateur" element={<UserPreferencesPage />} />
         <Route path="/foyer" element={<Navigate to="/parametres/foyer" replace />} />
       </Route>
       <Route

apps/web/src/api/client.ts

@@ -6,8 +6,10 @@ import {
   type HouseView,
   type LoginInput,
   type PlanningView,
+  type PreferencesView,
   type SafeUserProfile,
   type SignupInput,
+  type ThemePreference,
 } from "@batch-cooking/shared";
 
 /** Base URL of the API, configurable via `VITE_API_URL` (see `.env.example`). */
@@ -174,6 +176,16 @@ export class ApiClient {
       body: JSON.stringify({ allergyIds }),
     });
   }
+
+  /** Fetches the current user's personalization preferences — `theme` defaults to `"SYSTEM"` if never set. */
+  public getPreferences(): Promise<PreferencesView> {
+    return this.request("/preferences");
+  }
+
+  /** Sets the current user's theme preference. */
+  public updatePreferences(theme: ThemePreference): Promise<PreferencesView> {
+    return this.request("/preferences", { method: "PATCH", body: JSON.stringify({ theme }) });
+  }
 }
 
 /** Single shared instance — this client is stateless, no need for one per caller. */

apps/web/src/features/theme/ThemeContext.tsx

@@ -0,0 +1,89 @@
+import type { ThemePreference } from "@batch-cooking/shared";
+import { type ReactNode, createContext, useCallback, useContext, useEffect, useState } from "react";
+import { apiClient } from "../../api/client";
+import { useAuth } from "../auth/AuthContext";
+
+/** Shape of the theme state/actions exposed via {@link useTheme}. */
+interface ThemeContextValue {
+  /** The signed-in user's theme preference — `"SYSTEM"` (the default) for a logged-out visitor too, nothing to load a preference for. */
+  theme: ThemePreference;
+  /** Persists `theme` and applies it immediately. Throws `ApiError` on failure. */
+  setTheme: (theme: ThemePreference) => Promise<void>;
+}
+
+/** React context carrying {@link ThemeContextValue} — always accessed through {@link useTheme}, never directly. */
+const ThemeContext = createContext<ThemeContextValue | null>(null);
+
+/**
+ * Applies `theme` to the document. `SYSTEM` *removes* the override rather
+ * than setting a literal `"system"` value `_theme.scss` wouldn't recognize
+ * — with no `data-theme` attribute at all, its `prefers-color-scheme`
+ * media query decides instead, exactly the "system" behavior.
+ */
+function applyTheme(theme: ThemePreference) {
+  if (theme === "SYSTEM") {
+    delete document.documentElement.dataset.theme;
+  } else {
+    document.documentElement.dataset.theme = theme.toLowerCase();
+  }
+}
+
+/**
+ * Provides the signed-in user's theme preference and keeps the document in
+ * sync with it. Must be nested inside `AuthProvider` (reads `useAuth()`'s
+ * `user` to know when a profile is available to load a preference for) —
+ * see `main.tsx`.
+ *
+ * Keyed on `user?.id` rather than `user` itself: `AuthContext`'s `user`
+ * object is a fresh reference every time it refreshes (e.g. after an
+ * unrelated `refreshUser()` call elsewhere), which shouldn't re-trigger a
+ * preferences fetch — only actually signing in/out or switching accounts
+ * should.
+ */
+export function ThemeProvider({ children }: { children: ReactNode }) {
+  const { user } = useAuth();
+  const [theme, setThemeState] = useState<ThemePreference>("SYSTEM");
+
+  // biome-ignore lint/correctness/useExhaustiveDependencies: keyed on the id on purpose, see the doc comment above.
+  useEffect(() => {
+    if (!user) {
+      setThemeState("SYSTEM");
+      applyTheme("SYSTEM");
+      return;
+    }
+
+    let cancelled = false;
+    apiClient
+      .getPreferences()
+      .then((preferences) => {
+        if (cancelled) return;
+        setThemeState(preferences.theme);
+        applyTheme(preferences.theme);
+      })
+      // Failing to load a preference (e.g. a network hiccup) shouldn't break
+      // the rest of the app — worst case the theme just stays at its
+      // current/default value, same "not fatal" spirit as AuthContext's own
+      // `me()` call on mount.
+      .catch(() => {});
+    return () => {
+      cancelled = true;
+    };
+  }, [user?.id]);
+
+  const setTheme = useCallback(async (newTheme: ThemePreference) => {
+    await apiClient.updatePreferences(newTheme);
+    setThemeState(newTheme);
+    applyTheme(newTheme);
+  }, []);
+
+  return <ThemeContext.Provider value={{ theme, setTheme }}>{children}</ThemeContext.Provider>;
+}
+
+/** Reads the current theme state/actions. Must be called from within a {@link ThemeProvider}. */
+export function useTheme(): ThemeContextValue {
+  const ctx = useContext(ThemeContext);
+  if (!ctx) {
+    throw new Error("useTheme must be used within a ThemeProvider");
+  }
+  return ctx;
+}

apps/web/src/layouts/AppLayout.scss

@@ -15,7 +15,9 @@
 
 // Fixed-width nav rail. Its own surface (not the page background), same
 // elevation language as a card, so it reads as a distinct, permanent piece
-// of chrome rather than part of the scrolling content.
+// of chrome rather than part of the scrolling content. `width` transitions
+// so collapsing/expanding (see `.collapsed` below) reads as a deliberate
+// motion rather than an abrupt layout jump.
 .app-sidebar {
   display: flex;
   flex-direction: column;
@@ -24,13 +26,55 @@
   padding: var(--space-lg) var(--space-md);
   background: var(--color-surface);
   border-right: 1px solid var(--color-border);
+  transition: width 0.15s ease;
+
+  &__top {
+    display: flex;
+    align-items: center;
+    justify-content: space-between;
+    padding: 0 var(--space-sm) var(--space-xl);
+  }
 
   &__brand {
-    padding: 0 var(--space-sm) var(--space-xl);
+    display: flex;
+    align-items: center;
     font-family: var(--font-display);
     font-weight: 700;
     font-size: var(--font-size-lg);
     color: var(--color-primary);
+    overflow: hidden;
+    white-space: nowrap;
+  }
+
+  // Full wordmark by default; swapped for a short monogram when collapsed
+  // (see `.collapsed &__brand-full`/`&__brand-mark` below) — clearer than
+  // an arbitrary icon standing in for the brand itself.
+  &__brand-mark {
+    display: none;
+  }
+
+  &__collapse-toggle {
+    width: 1.75rem;
+    height: 1.75rem;
+    flex-shrink: 0;
+    display: grid;
+    place-items: center;
+    border: 1px solid var(--color-border);
+    border-radius: var(--radius-base);
+    background: var(--color-surface);
+    color: var(--color-text-muted);
+    cursor: pointer;
+
+    svg {
+      width: 1rem;
+      height: 1rem;
+      transition: transform 0.15s ease;
+    }
+
+    &:hover {
+      background: var(--color-surface-alt);
+      color: var(--color-text);
+    }
   }
 
   &__nav {
@@ -40,12 +84,23 @@
     gap: var(--space-xs);
 
     a {
+      display: flex;
+      align-items: center;
+      gap: var(--space-sm);
       padding: var(--space-sm);
       border-radius: var(--radius-base);
       color: var(--color-text);
       font-weight: 600;
       font-size: var(--font-size-sm);
       text-decoration: none;
+      white-space: nowrap;
+      overflow: hidden;
+
+      svg {
+        flex-shrink: 0;
+        width: 1.25rem;
+        height: 1.25rem;
+      }
 
       &:hover {
         background: var(--color-surface-alt);
@@ -87,6 +142,19 @@
     }
   }
 
+  &__settings-toggle-left {
+    display: flex;
+    align-items: center;
+    gap: var(--space-sm);
+    overflow: hidden;
+
+    svg {
+      flex-shrink: 0;
+      width: 1.25rem;
+      height: 1.25rem;
+    }
+  }
+
   &__settings-nav {
     margin-top: var(--space-xs);
   }
@@ -99,8 +167,11 @@
   }
 
   &__account-toggle {
+    display: flex;
+    align-items: center;
+    gap: var(--space-sm);
     width: 100%;
-    padding: 0.5rem var(--space-sm);
+    padding: 0.4rem var(--space-sm);
     font-family: var(--font-body);
     font-size: var(--font-size-sm);
     font-weight: 600;
@@ -110,12 +181,27 @@
     border: 1px solid var(--color-border);
     background: var(--color-surface);
     color: var(--color-text);
+    overflow: hidden;
+    white-space: nowrap;
 
     &:hover {
       background: var(--color-surface-alt);
     }
   }
 
+  &__avatar {
+    flex-shrink: 0;
+    width: 1.5rem;
+    height: 1.5rem;
+    display: grid;
+    place-items: center;
+    border-radius: 50%;
+    background: var(--color-primary);
+    color: #fff;
+    font-size: var(--font-size-xs);
+    font-weight: 700;
+  }
+
   // Anchored just above the toggle rather than inline in the flow — it's a
   // transient overlay, not part of the sidebar's permanent layout.
   &__account-menu {
@@ -143,12 +229,68 @@
       background: none;
       border: none;
       cursor: pointer;
+      white-space: nowrap;
 
       &:hover {
         background: var(--color-surface-alt);
       }
     }
   }
+
+  // --- Collapsed (icon-only rail) state -----------------------------------
+  // A single class toggle on the root element — every nested rule below
+  // just hides labels/chevrons and re-centers icons via CSS, no child
+  // component needs to know the sidebar is collapsed.
+  &.collapsed {
+    width: 4.25rem;
+    padding-left: var(--space-sm);
+    padding-right: var(--space-sm);
+
+    .app-sidebar__top {
+      flex-direction: column;
+      gap: var(--space-sm);
+      padding-left: 0;
+      padding-right: 0;
+    }
+
+    .app-sidebar__brand-full {
+      display: none;
+    }
+
+    .app-sidebar__brand-mark {
+      display: block;
+    }
+
+    .app-sidebar__collapse-toggle svg {
+      transform: rotate(180deg);
+    }
+
+    .app-sidebar__nav a,
+    .app-sidebar__settings-toggle,
+    .app-sidebar__account-toggle {
+      justify-content: center;
+      padding-left: 0;
+      padding-right: 0;
+    }
+
+    .app-sidebar__settings-toggle-left {
+      gap: 0;
+    }
+
+    .label,
+    .chevron {
+      display: none;
+    }
+
+    // The popover would otherwise shrink to the icon rail's own width,
+    // squashing "Mon compte"/"Se déconnecter" — give it a normal,
+    // comfortable width instead, still anchored to the rail's left edge.
+    .app-sidebar__account-menu {
+      left: 0;
+      right: auto;
+      width: 12rem;
+    }
+  }
 }
 
 .app-content {
@@ -176,10 +318,14 @@
     border-right: none;
     border-bottom: 1px solid var(--color-border);
 
-    &__brand {
+    &__top {
       padding: 0 var(--space-sm) 0 0;
     }
 
+    &__brand {
+      padding: 0;
+    }
+
     &__nav {
       flex-direction: row;
       overflow-x: auto;

apps/web/src/layouts/AppLayout.tsx

@@ -3,6 +3,20 @@ import { useTranslation } from "react-i18next";
 import { NavLink, Outlet, useLocation, useNavigate } from "react-router-dom";
 import { useAuth } from "../features/auth/AuthContext";
 import "./AppLayout.scss";
+import {
+  AccountIcon,
+  ChevronLeftIcon,
+  DietPreferencesIcon,
+  HouseholdIcon,
+  PlanningIcon,
+  RecipesIcon,
+  SettingsIcon,
+  ShoppingListIcon,
+  UserPreferencesIcon,
+} from "./nav-icons";
+
+/** `localStorage` key persisting {@link AppLayout}'s collapsed/expanded sidebar state across reloads. */
+const SIDEBAR_COLLAPSED_KEY = "batchcooking:sidebarCollapsed";
 
 /**
  * One entry in the sidebar's main nav. `key` maps to `layout.nav.<key>` in
@@ -10,9 +24,9 @@ import "./AppLayout.scss";
  * one locale key, no other file to touch.
  */
 const NAV_ITEMS = [
-  { to: "/", key: "planning" },
-  { to: "/recettes", key: "recipes" },
-  { to: "/liste-de-courses", key: "shoppingList" },
+  { to: "/", key: "planning", Icon: PlanningIcon },
+  { to: "/recettes", key: "recipes", Icon: RecipesIcon },
+  { to: "/liste-de-courses", key: "shoppingList", Icon: ShoppingListIcon },
 ] as const;
 
 /**
@@ -20,9 +34,10 @@ const NAV_ITEMS = [
  * maps to `layout.settings.nav.<key>`.
  */
 const SETTINGS_ITEMS = [
-  { to: "/parametres/compte", key: "account" },
-  { to: "/parametres/preferences", key: "preferences" },
-  { to: "/parametres/foyer", key: "household" },
+  { to: "/parametres/compte", key: "account", Icon: AccountIcon },
+  { to: "/parametres/preferences", key: "preferences", Icon: DietPreferencesIcon },
+  { to: "/parametres/foyer", key: "household", Icon: HouseholdIcon },
+  { to: "/parametres/preferences-utilisateur", key: "userPreferences", Icon: UserPreferencesIcon },
 ] as const;
 
 /**
@@ -30,20 +45,52 @@ const SETTINGS_ITEMS = [
  * collapsible "Paramètres" nav, and the account menu at the bottom) plus a
  * main content area rendering the matched child route via `<Outlet />`.
  *
+ * The sidebar itself can be collapsed to an icon-only rail (see
+ * `isCollapsed`/`SIDEBAR_COLLAPSED_KEY`) — every nav item keeps its icon
+ * and gains a `title` tooltip, its label just hides via CSS
+ * (`.app-sidebar.collapsed .label`, see AppLayout.scss), so collapsing is a
+ * single class toggle on the `<aside>`, not something each child component
+ * needs to know about.
+ *
  * Mounted once as the parent element of the whole authenticated route
  * group, itself wrapped in {@link RequireAuth} (see `App.tsx`) — `user` is
  * therefore guaranteed non-null by the time this renders.
  */
 export function AppLayout() {
   const { t } = useTranslation();
+  const [isCollapsed, setIsCollapsed] = useState(
+    () => localStorage.getItem(SIDEBAR_COLLAPSED_KEY) === "true",
+  );
+
+  function toggleCollapsed() {
+    setIsCollapsed((collapsed) => {
+      const next = !collapsed;
+      localStorage.setItem(SIDEBAR_COLLAPSED_KEY, String(next));
+      return next;
+    });
+  }
 
   return (
     <div className="app-layout">
-      <aside className="app-sidebar">
-        <div className="app-sidebar__brand">batchCooking</div>
+      <aside className={isCollapsed ? "app-sidebar collapsed" : "app-sidebar"}>
+        <div className="app-sidebar__top">
+          <div className="app-sidebar__brand">
+            {/* Collapsed: a short monogram instead of the full wordmark — clearer than an arbitrary icon standing in for the brand itself. */}
+            <span className="app-sidebar__brand-full">batchCooking</span>
+            <span className="app-sidebar__brand-mark">bC</span>
+          </div>
+          <button
+            type="button"
+            className="app-sidebar__collapse-toggle"
+            onClick={toggleCollapsed}
+            title={t(isCollapsed ? "layout.sidebar.expand" : "layout.sidebar.collapse")}
+          >
+            <ChevronLeftIcon />
+          </button>
+        </div>
 
         <nav className="app-sidebar__nav">
-          {NAV_ITEMS.map(({ to, key }) => (
+          {NAV_ITEMS.map(({ to, key, Icon }) => (
             <NavLink
               key={to}
               to={to}
@@ -53,8 +100,10 @@ export function AppLayout() {
               // same way `end` would.
               end={to === "/"}
               className={({ isActive }) => (isActive ? "active" : undefined)}
+              title={t(`layout.nav.${key}`)}
             >
-              {t(`layout.nav.${key}`)}
+              <Icon />
+              <span className="label">{t(`layout.nav.${key}`)}</span>
             </NavLink>
           ))}
         </nav>
@@ -71,12 +120,16 @@ export function AppLayout() {
 }
 
 /**
- * Collapsible "Paramètres" section revealing the three settings pages
- * (Compte/Préférences/Foyer — see `pages/settings/`). Starts open whenever
- * the current route is already under `/parametres`, so following a link
- * there (e.g. from {@link AccountMenu}) doesn't land on a collapsed menu;
- * otherwise starts closed to keep the sidebar's main focus on the primary
- * nav above it.
+ * Collapsible "Paramètres" section revealing the settings pages (Compte /
+ * Préférences alimentaires / Foyer / Préférences utilisateur — see
+ * `pages/settings/`). Starts open whenever the current route is already
+ * under `/parametres`, so following a link there (e.g. from
+ * {@link AccountMenu}) doesn't land on a collapsed menu; otherwise starts
+ * closed to keep the sidebar's main focus on the primary nav above it.
+ *
+ * Independent of the whole-sidebar collapse toggle in {@link AppLayout} —
+ * this menu's own open/closed state persists across that (a rail-collapsed
+ * sidebar can still have "Paramètres" expanded, just showing icons).
  */
 function SettingsMenu() {
   const { t } = useTranslation();
@@ -90,20 +143,28 @@ function SettingsMenu() {
         className="app-sidebar__settings-toggle"
         aria-expanded={isOpen}
         onClick={() => setIsOpen((open) => !open)}
+        title={t("layout.settings.toggle")}
       >
-        {t("layout.settings.toggle")}
-        <span aria-hidden="true">{isOpen ? "▾" : "▸"}</span>
+        <span className="app-sidebar__settings-toggle-left">
+          <SettingsIcon />
+          <span className="label">{t("layout.settings.toggle")}</span>
+        </span>
+        <span className="chevron" aria-hidden="true">
+          {isOpen ? "▾" : "▸"}
+        </span>
       </button>
 
       {isOpen && (
         <nav className="app-sidebar__nav app-sidebar__settings-nav">
-          {SETTINGS_ITEMS.map(({ to, key }) => (
+          {SETTINGS_ITEMS.map(({ to, key, Icon }) => (
             <NavLink
               key={to}
               to={to}
               className={({ isActive }) => (isActive ? "active" : undefined)}
+              title={t(`layout.settings.nav.${key}`)}
             >
-              {t(`layout.settings.nav.${key}`)}
+              <Icon />
+              <span className="label">{t(`layout.settings.nav.${key}`)}</span>
             </NavLink>
           ))}
         </nav>
@@ -132,6 +193,8 @@ function AccountMenu() {
     navigate("/login");
   }
 
+  const initial = user?.firstName?.charAt(0).toUpperCase() ?? "";
+
   return (
     <div className="app-sidebar__footer">
       <button
@@ -139,8 +202,12 @@ function AccountMenu() {
         className="app-sidebar__account-toggle"
         aria-expanded={isOpen}
         onClick={() => setIsOpen((open) => !open)}
+        title={t("layout.greeting", { firstName: user?.firstName })}
       >
-        {t("layout.greeting", { firstName: user?.firstName })}
+        <span className="app-sidebar__avatar" aria-hidden="true">
+          {initial}
+        </span>
+        <span className="label">{t("layout.greeting", { firstName: user?.firstName })}</span>
       </button>
 
       {isOpen && (

apps/web/src/layouts/nav-icons.tsx

@@ -0,0 +1,110 @@
+import type { ReactNode } from "react";
+
+// Small, hand-drawn line-icon set for the sidebar nav (24×24 viewBox,
+// matches the reviewed mockup — see the plan/PR description) rather than
+// pulling in an icon library for a handful of glyphs. Sized entirely via
+// CSS (`.app-sidebar__nav svg` etc., see AppLayout.scss) — no width/height
+// attribute here, so the same markup works at any size the caller picks.
+// `aria-hidden` on every icon: each one is always paired with visible text
+// (the nav label, or a `title` tooltip when collapsed) that already
+// conveys the meaning — the icon itself is decorative.
+
+function Icon({ children }: { children: ReactNode }) {
+  return (
+    <svg
+      viewBox="0 0 24 24"
+      fill="none"
+      stroke="currentColor"
+      strokeWidth="2"
+      strokeLinecap="round"
+      strokeLinejoin="round"
+      aria-hidden="true"
+    >
+      {children}
+    </svg>
+  );
+}
+
+export function PlanningIcon() {
+  return (
+    <Icon>
+      <rect x="3" y="4" width="18" height="18" rx="2" />
+      <path d="M16 2v4M8 2v4M3 10h18" />
+    </Icon>
+  );
+}
+
+export function RecipesIcon() {
+  return (
+    <Icon>
+      <path d="M4 19.5A2.5 2.5 0 0 1 6.5 17H20" />
+      <path d="M6.5 2H20v20H6.5A2.5 2.5 0 0 1 4 19.5v-15A2.5 2.5 0 0 1 6.5 2z" />
+    </Icon>
+  );
+}
+
+export function ShoppingListIcon() {
+  return (
+    <Icon>
+      <circle cx="9" cy="21" r="1" />
+      <circle cx="20" cy="21" r="1" />
+      <path d="M1 1h4l2.68 13.39a2 2 0 0 0 2 1.61h9.72a2 2 0 0 0 2-1.61L23 6H6" />
+    </Icon>
+  );
+}
+
+export function SettingsIcon() {
+  return (
+    <Icon>
+      <circle cx="12" cy="12" r="3" />
+      <path d="M19.4 15a1.65 1.65 0 0 0 .33 1.82l.06.06a2 2 0 1 1-2.83 2.83l-.06-.06a1.65 1.65 0 0 0-1.82-.33 1.65 1.65 0 0 0-1 1.51V21a2 2 0 0 1-4 0v-.09A1.65 1.65 0 0 0 9 19.4a1.65 1.65 0 0 0-1.82.33l-.06.06a2 2 0 1 1-2.83-2.83l.06-.06a1.65 1.65 0 0 0 .33-1.82 1.65 1.65 0 0 0-1.51-1H3a2 2 0 0 1 0-4h.09A1.65 1.65 0 0 0 4.6 9a1.65 1.65 0 0 0-.33-1.82l-.06-.06a2 2 0 1 1 2.83-2.83l.06.06a1.65 1.65 0 0 0 1.82.33H9a1.65 1.65 0 0 0 1-1.51V3a2 2 0 0 1 4 0v.09a1.65 1.65 0 0 0 1 1.51 1.65 1.65 0 0 0 1.82-.33l.06-.06a2 2 0 1 1 2.83 2.83l-.06.06a1.65 1.65 0 0 0-.33 1.82V9a1.65 1.65 0 0 0 1.51 1H21a2 2 0 0 1 0 4h-.09a1.65 1.65 0 0 0-1.51 1z" />
+    </Icon>
+  );
+}
+
+export function AccountIcon() {
+  return (
+    <Icon>
+      <path d="M20 21v-2a4 4 0 0 0-4-4H8a4 4 0 0 0-4 4v2" />
+      <circle cx="12" cy="7" r="4" />
+    </Icon>
+  );
+}
+
+export function DietPreferencesIcon() {
+  return (
+    <Icon>
+      <path d="M11 20A7 7 0 0 1 9.8 6.1C15.5 5 17 4.48 19 2c1 2 2 4.18 2 8 0 5.5-4.78 10-10 10z" />
+      <path d="M2 21c0-3 1.85-5.36 5.08-6C9.5 14.52 12 13 13 12" />
+    </Icon>
+  );
+}
+
+export function HouseholdIcon() {
+  return (
+    <Icon>
+      <path d="M3 9l9-7 9 7v11a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2z" />
+      <path d="M9 22V12h6v10" />
+    </Icon>
+  );
+}
+
+export function UserPreferencesIcon() {
+  return (
+    <Icon>
+      <circle cx="13.5" cy="6.5" r=".5" />
+      <circle cx="17.5" cy="10.5" r=".5" />
+      <circle cx="8.5" cy="7.5" r=".5" />
+      <circle cx="6.5" cy="12.5" r=".5" />
+      <path d="M12 2C6.5 2 2 6.5 2 12s4.5 10 10 10c.9 0 1.5-.7 1.5-1.5 0-.4-.2-.8-.4-1.1-.2-.3-.4-.6-.4-1 0-.8.7-1.5 1.5-1.5H16c3.3 0 6-2.7 6-6 0-4.4-4-8-10-8z" />
+    </Icon>
+  );
+}
+
+export function ChevronLeftIcon() {
+  return (
+    <Icon>
+      <path d="M15 18l-6-6 6-6" />
+    </Icon>
+  );
+}

apps/web/src/locales/fr/translation.json

@@ -59,6 +59,10 @@
     }
   },
   "layout": {
+    "sidebar": {
+      "collapse": "Replier le menu",
+      "expand": "Déplier le menu"
+    },
     "nav": {
       "planning": "Planning",
       "recipes": "Recettes",
@@ -68,8 +72,9 @@
       "toggle": "Paramètres",
       "nav": {
         "account": "Compte",
-        "preferences": "Préférences",
-        "household": "Foyer"
+        "preferences": "Préférences alimentaires",
+        "household": "Foyer",
+        "userPreferences": "Préférences utilisateur"
       }
     },
     "accountMenu": {
@@ -145,6 +150,15 @@
       "intolerancesLabel": "Intolérances"
     }
   },
+  "userPreferences": {
+    "title": "Préférences utilisateur",
+    "themeLabel": "Thème",
+    "theme": {
+      "LIGHT": "Clair",
+      "DARK": "Sombre",
+      "SYSTEM": "Système"
+    }
+  },
   "household": {
     "title": "Foyer",
     "form": {

apps/web/src/main.tsx

@@ -3,6 +3,7 @@ import { createRoot } from "react-dom/client";
 import { BrowserRouter } from "react-router-dom";
 import { App } from "./App";
 import { AuthProvider } from "./features/auth/AuthContext";
+import { ThemeProvider } from "./features/theme/ThemeContext";
 // Side-effect import: initializes the i18next instance before anything
 // renders (react-i18next reads it via context under the hood). See i18n/i18n.ts.
 import "./i18n/i18n";
@@ -19,7 +20,9 @@ createRoot(rootElement).render(
   <StrictMode>
     <BrowserRouter>
       <AuthProvider>
-        <App />
+        <ThemeProvider>
+          <App />
+        </ThemeProvider>
       </AuthProvider>
     </BrowserRouter>
   </StrictMode>,

apps/web/src/pages/settings/UserPreferencesPage.tsx

@@ -0,0 +1,66 @@
+import { ErrorCode, THEME_PREFERENCES, type ThemePreference } from "@batch-cooking/shared";
+import { useState } from "react";
+import { useTranslation } from "react-i18next";
+import { ApiError } from "../../api/client";
+import { useTheme } from "../../features/theme/ThemeContext";
+import { errorMessageService } from "../../services/error-message.service";
+import "./settings-pages.scss";
+
+/** Status of the theme choice's own autosave — see `PreferencesPage` for the same hot-saving pattern. */
+type SaveState = "idle" | "saving" | "saved" | "error";
+
+/**
+ * User (personalization) preferences — routed at
+ * `/parametres/preferences-utilisateur`. Just the theme choice for now
+ * (light/dark/system — see `features/theme/ThemeContext.tsx`), meant to
+ * grow. Distinct from `/parametres/preferences` ("Préférences
+ * alimentaires" — regime/allergies): that page is about the household's
+ * food constraints, this one is about how the app itself looks, unrelated
+ * concerns that happened to share a name before this page existed.
+ */
+export function UserPreferencesPage() {
+  const { t } = useTranslation();
+  const { theme, setTheme } = useTheme();
+  const [saveState, setSaveState] = useState<SaveState>("idle");
+  const [saveError, setSaveError] = useState<string | null>(null);
+
+  async function handleChange(newTheme: ThemePreference) {
+    setSaveState("saving");
+    try {
+      await setTheme(newTheme);
+      setSaveState("saved");
+    } catch (err) {
+      const code = err instanceof ApiError ? err.code : ErrorCode.INTERNAL_ERROR;
+      setSaveError(errorMessageService.getLabel(code));
+      setSaveState("error");
+    }
+  }
+
+  return (
+    <div className="settings-page">
+      <h1>{t("userPreferences.title")}</h1>
+
+      <div className="settings-page__section">
+        <fieldset className="theme-select">
+          <legend>{t("userPreferences.themeLabel")}</legend>
+          {THEME_PREFERENCES.map((option) => (
+            <label key={option} className="theme-select__option">
+              <input
+                type="radio"
+                name="theme"
+                value={option}
+                checked={theme === option}
+                onChange={() => handleChange(option)}
+              />
+              {t(`userPreferences.theme.${option}`)}
+            </label>
+          ))}
+        </fieldset>
+
+        {saveState === "saving" && <p className="settings-page__saving">{t("common.saving")}</p>}
+        {saveState === "saved" && <p className="settings-page__saved">{t("common.saved")}</p>}
+        {saveState === "error" && <p className="field-error">{saveError}</p>}
+      </div>
+    </div>
+  );
+}

apps/web/src/pages/settings/settings-pages.scss

@@ -149,3 +149,26 @@ button.settings-page__link-button {
   cursor: pointer;
   text-decoration: underline;
 }
+
+// Theme choice (UserPreferencesPage) — a plain radio group, no fieldset/
+// legend styling exists elsewhere yet to reuse (AllergySelect's `.allergy-
+// select` in profile-forms.scss is checkbox-grid specific).
+.theme-select {
+  border: none;
+  padding: 0;
+  margin: 0;
+
+  legend {
+    padding: 0 0 var(--space-sm);
+    font-weight: 600;
+    font-size: var(--font-size-sm);
+  }
+
+  &__option {
+    display: flex;
+    align-items: center;
+    gap: var(--space-sm);
+    padding: var(--space-xs) 0;
+    cursor: pointer;
+  }
+}

apps/web/src/styles/_theme.scss

@@ -107,9 +107,9 @@
 
 // --- Dark mode ---------------------------------------------------------
 // Follows the OS/browser preference by default. Guarded with
-// `:root:not([data-theme="light"])` so that, if a manual theme switch is
-// ever added, an explicit "light" choice can override a dark OS setting —
-// today nothing sets `data-theme`, so this simply tracks system preference.
+// `:root:not([data-theme="light"])` so an explicit "light" choice (see
+// apps/web's `ThemeContext`, `SYSTEM` = no `data-theme` attribute at all —
+// this block then decides) can override a dark OS setting.
 @media (prefers-color-scheme: dark) {
   :root:not([data-theme="light"]) {
     --color-background: #14181a;
@@ -138,8 +138,9 @@
   }
 }
 
-// Mirrors the block above for a future explicit "dark" choice (e.g. a
-// theme toggle), so it wins over the OS setting in both directions.
+// Mirrors the block above for an explicit "dark" choice (`ThemeContext`
+// sets `data-theme="dark"` on `<html>`), so it wins over the OS setting in
+// both directions.
 :root[data-theme="dark"] {
   --color-background: #14181a;
   --color-surface: #1c221e;

packages/shared/src/index.ts

@@ -8,9 +8,11 @@ export * from "./schemas/account.js";
 export * from "./schemas/auth.js";
 export * from "./schemas/household.js";
 export * from "./schemas/planning.js";
+export * from "./schemas/preferences.js";
 export * from "./schemas/profile.js";
 export * from "./tools/assert-is-never.js";
 export * from "./types/household.js";
 export * from "./types/planning.js";
+export * from "./types/preferences.js";
 export * from "./types/reference.js";
 export * from "./types/user-profile.js";

packages/shared/src/schemas/preferences.ts

@@ -0,0 +1,11 @@
+import { z } from "zod";
+import { THEME_PREFERENCES } from "../types/preferences.js";
+
+// See schemas/auth.ts for the shared client/server validation rationale.
+
+/** Payload accepted by `PATCH /preferences`. */
+export const updatePreferencesSchema = z.object({
+  theme: z.enum(THEME_PREFERENCES),
+});
+/** Inferred TS type for {@link updatePreferencesSchema}'s validated output. */
+export type UpdatePreferencesInput = z.infer<typeof updatePreferencesSchema>;

packages/shared/src/types/preferences.ts

@@ -0,0 +1,15 @@
+/**
+ * The 3 values a profile's theme preference can take — `SYSTEM` means "no
+ * explicit choice, follow the OS/browser preference" (see `apps/web`'s
+ * `ThemeContext`, which maps this to *not* setting the `data-theme`
+ * attribute at all, letting `_theme.scss`'s `prefers-color-scheme` media
+ * query take over).
+ */
+export const THEME_PREFERENCES = ["LIGHT", "DARK", "SYSTEM"] as const;
+/** Inferred TS type for one {@link THEME_PREFERENCES} member. */
+export type ThemePreference = (typeof THEME_PREFERENCES)[number];
+
+/** A profile's personalization preferences, as returned by `GET /preferences` / `PATCH /preferences`. */
+export interface PreferencesView {
+  theme: ThemePreference;
+}