fix(chat): Reset model selection when starting new conversation

lib/features/chat/views/chat_page.dart

@@ -130,6 +130,10 @@ class _ChatPageState extends ConsumerState<ChatPage> {
     // Clear any pending folder selection
     ref.read(pendingFolderIdProvider.notifier).clear();
 
+    // Reset to default model for new conversations (fixes #296)
+    ref.read(isManualModelSelectionProvider.notifier).set(false);
+    ref.invalidate(defaultModelProvider);
+
     // Scroll to top
     if (_scrollController.hasClients) {
       _scrollController.jumpTo(0);