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/(main)/trash/page.tsx

@@ -0,0 +1,23 @@
+import { ArchiveHeader } from '@/components/archive-header'
+import { Trash2 } from 'lucide-react'
+
+export const dynamic = 'force-dynamic'
+
+export default function TrashPage() {
+    // Currently, we don't have soft-delete implemented, so trash is always empty.
+    // This page exists to fix the 404 error and provide a placeholder.
+
+    return (
+        <main className="container mx-auto px-4 py-8 max-w-7xl">
+            <div className="flex flex-col items-center justify-center min-h-[60vh] text-center text-gray-500">
+                <div className="bg-gray-100 dark:bg-gray-800 p-6 rounded-full mb-4">
+                    <Trash2 className="w-12 h-12 text-gray-400" />
+                </div>
+                <h2 className="text-xl font-medium mb-2">La corbeille est vide</h2>
+                <p className="max-w-md text-sm opacity-80">
+                    Les notes supprimées sont actuellement effacées définitivement.
+                </p>
+            </div>
+        </main>
+    )
+}