feat(feed): add scroll-to-top on feed tab re-tap

Tapping the feed tab while already on the feed screen now scrolls the
current feed to the top, matching common social media app behavior.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[e-mail]>

lib/screens/home/feed_screen.dart

···
   final VoidCallback? onSearchTap;
 
   @override
-  State<FeedScreen> createState() => _FeedScreenState();
+  State<FeedScreen> createState() => FeedScreenState();
 }
 
-class _FeedScreenState extends State<FeedScreen> {
+class FeedScreenState extends State<FeedScreen> {
   late PageController _pageController;
   final Map<FeedType, ScrollController> _scrollControllers = {};
   late AuthProvider _authProvider;
···
           controller.position.maxScrollExtent - 200) {
         context.read<MultiFeedProvider>().loadMore(type);
       }
+    }
+  }
+
+  /// Scroll the current feed to the top with animation
+  void scrollToTop() {
+    final currentFeed = context.read<MultiFeedProvider>().currentFeedType;
+    final controller = _scrollControllers[currentFeed];
+    if (controller != null && controller.hasClients) {
+      controller.animateTo(
+        0,
+        duration: const Duration(milliseconds: 300),
+        curve: Curves.easeOut,
+      );
     }
   }
 

lib/screens/home/main_shell_screen.dart

···
 
 class _MainShellScreenState extends State<MainShellScreen> {
   int _selectedIndex = 0;
+  final _feedScreenKey = GlobalKey<FeedScreenState>();
 
   void _onItemTapped(int index) {
+    // If already on feed tab, scroll to top
+    if (index == 0 && _selectedIndex == 0) {
+      _feedScreenKey.currentState?.scrollToTop();
+      return;
+    }
     setState(() {
       _selectedIndex = index;
     });
···
       body: IndexedStack(
         index: _selectedIndex,
         children: [
-          FeedScreen(onSearchTap: _onCommunitiesTap),
+          FeedScreen(key: _feedScreenKey, onSearchTap: _onCommunitiesTap),
           const CommunitiesScreen(),
           CreatePostScreen(onNavigateToFeed: _onNavigateToFeed),
           const NotificationsScreen(),