improve asnyc loading and error widgets

app/lib/features/web_feed/presentation/screens/feed_article_list.dart

@@ -190,7 +190,7 @@ class FeedArticleListScreen extends HookConsumerWidget {
               exception: error,
             ),
           ),
-          loading: () => const SizedBox.shrink(),
+          loading: () => const Center(child: CircularProgressIndicator()),
         ),
       ),
     );

app/lib/features/web_feed/presentation/screens/feed_list.dart

@@ -93,7 +93,7 @@ class FeedListScreen extends HookConsumerWidget {
             },
           ),
         ),
-        loading: () => const SizedBox.shrink(),
+        loading: () => const Center(child: CircularProgressIndicator()),
       ),
       floatingActionButton: FloatingActionButton.extended(
         label: const Text('Feed'),

app/lib/features/web_feed/presentation/widgets/feed_card.dart

@@ -146,7 +146,13 @@ class FeedCard extends HookConsumerWidget {
                           );
                         },
                         error: (error, stackTrace) => const Text('N/A'),
-                        loading: () => const SizedBox.shrink(),
+                        loading: () => const SizedBox(
+                          height: 16,
+                          width: 16,
+                          child: Center(
+                            child: CircularProgressIndicator(strokeWidth: 2),
+                          ),
+                        ),
                       );
                     },
                   ),