fix: unify theme system - fix theme switching persistence

- Unified localStorage key to 'theme-preference' across all components
- Fixed header.tsx using wrong localStorage key ('theme' instead of 'theme-preference')
- Added localStorage hybrid persistence for instant theme changes
- Removed router.refresh() which was causing stale data revert
- Replaced Blue theme with Sepia
- Consolidated auth() calls to prevent race conditions
- Updated UserSettingsData types to include all themes

keep-notes/app/(auth)/layout.tsx

@@ -1,13 +1,19 @@
+'use client';
+
+import { LanguageProvider } from '@/lib/i18n/LanguageProvider';
+
 export default function AuthLayout({
   children,
 }: Readonly<{
   children: React.ReactNode;
 }>) {
   return (
-    <div className="flex min-h-screen items-center justify-center bg-gray-50 dark:bg-zinc-950">
-      <div className="w-full max-w-md p-4">
-        {children}
+    <LanguageProvider initialLanguage="fr">
+      <div className="flex min-h-screen items-center justify-center bg-gray-50 dark:bg-zinc-950">
+        <div className="w-full max-w-md p-4">
+          {children}
+        </div>
       </div>
-    </div>
+    </LanguageProvider>
   );
 }