Web: UserPreferencesPage (thème) + renommage "Préférences alimentaires" (step 3/4)

- ThemeContext (features/theme/) : charge/applique le thème du profil
  connecté via l'attribut data-theme (SYSTEM = pas d'attribut, laisse
  la media query prefers-color-scheme décider) ; échec réseau non
  bloquant (worst case reste au thème courant, pas d'unhandled rejection)
- UserPreferencesPage, routée /parametres/preferences-utilisateur,
  hot-save (3 boutons radio Clair/Sombre/Système)
- layout.settings.nav.preferences renommé "Préférences alimentaires"
  (évite la confusion avec ce nouveau concept plus large), nouvelle
  entrée "Préférences utilisateur"
- _theme.scss: commentaires mis à jour (l'attribut data-theme est
  désormais réellement posé, plus une simple anticipation)

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.tsx

@@ -23,6 +23,7 @@ const SETTINGS_ITEMS = [
   { to: "/parametres/compte", key: "account" },
   { to: "/parametres/preferences", key: "preferences" },
   { to: "/parametres/foyer", key: "household" },
+  { to: "/parametres/preferences-utilisateur", key: "userPreferences" },
 ] as const;
 
 /**
@@ -71,8 +72,9 @@ export function AppLayout() {
 }
 
 /**
- * Collapsible "Paramètres" section revealing the three settings pages
- * (Compte/Préférences/Foyer — see `pages/settings/`). Starts open whenever
+ * 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

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

@@ -68,8 +68,9 @@
       "toggle": "Paramètres",
       "nav": {
         "account": "Compte",
-        "preferences": "Préférences",
-        "household": "Foyer"
+        "preferences": "Préférences alimentaires",
+        "household": "Foyer",
+        "userPreferences": "Préférences utilisateur"
       }
     },
     "accountMenu": {
@@ -145,6 +146,15 @@
       "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;