fix(headlines-feed): prevent remote config null access on feed page

- Add a check for remoteConfig availability in AppBloc
- Display a loading indicator while remoteConfig is null
- This fix addresses a null access error that occurs after
  authentication and before remote config is fetched

Author: fulleni

lib/headlines-feed/view/headlines_feed_page.dart

@@ -153,6 +153,20 @@ class _HeadlinesFeedPageState extends State<HeadlinesFeedPage> {
         ),
         body: BlocBuilder<HeadlinesFeedBloc, HeadlinesFeedState>(
           builder: (context, state) {
+            // Access the AppBloc to check for remoteConfig availability.
+            final appBlocState = context.watch<AppBloc>().state;
+
+            // If remoteConfig is not yet loaded, show a loading indicator.
+            // This handles the brief period after authentication but before
+            // the remote config is fetched, preventing null access errors.
+            if (appBlocState.remoteConfig == null) {
+              return LoadingStateWidget(
+                icon: Icons.settings_applications_outlined,
+                headline: l10n.headlinesFeedLoadingHeadline,
+                subheadline: l10n.pleaseWait,
+              );
+            }
+
             if (state.status == HeadlinesFeedStatus.initial ||
                 (state.status == HeadlinesFeedStatus.loading &&
                     state.feedItems.isEmpty)) {
@@ -187,8 +201,8 @@ class _HeadlinesFeedPageState extends State<HeadlinesFeedPage> {
                     const SizedBox(height: AppSpacing.lg),
                     ElevatedButton(
                       onPressed: () => context.read<HeadlinesFeedBloc>().add(
-                            HeadlinesFeedFiltersCleared(),
-                          ),
+                        HeadlinesFeedFiltersCleared(),
+                      ),
                       child: Text(l10n.headlinesFeedClearFiltersButton),
                     ),
                   ],