feat(headlines-feed): enhance user content preferences fetching

- Add `userId` parameter to `read` method in demo environment
- Improve scoping of user-specific data in DataInMemory
- Maintain backward compatibility for development/production environments

Author: fulleni

lib/headlines-feed/bloc/headlines_feed_bloc.dart

@@ -349,7 +349,13 @@ class HeadlinesFeedBloc extends Bloc<HeadlinesFeedEvent, HeadlinesFeedState> {
 
       // Fetch user content preferences to get followed items for filtering suggestions.
       final userPreferences = currentUser?.id != null
-          ? await _userContentPreferencesRepository.read(id: currentUser!.id)
+          ? await _userContentPreferencesRepository.read(
+              id: currentUser!.id,
+              // In the demo environment, `DataInMemory` requires `userId` for correct
+              // scoping of user-specific data. In development/production, the backend
+              // handles this scoping, making `userId` optional at the client level.
+              userId: currentUser.id,
+            )
           : null;
 
       // Use the full decoration pipeline, which includes injecting a