refactor: update folders provider to use keepAlive for improved state management

- Changed the folders provider annotation to `@Riverpod(keepAlive: true)` to enhance state retention.
- This update aligns with recent improvements in state management across the application, ensuring better performance and user experience.

lib/core/providers/app_providers.dart

@@ -1564,7 +1564,7 @@ final webSearchAvailableProvider = Provider<bool>((ref) {
 });
 
 // Folders provider
-@riverpod
+@Riverpod(keepAlive: true)
 Future<List<Folder>> folders(Ref ref) async {
   // Protected: require authentication
   if (!ref.read(isAuthenticatedProvider2)) {