refactor: enhance chat message handling and scrolling behavior

- Added `sendMessageWithContainer` function to facilitate message sending with a ProviderContainer.
- Updated `_ChatPageState` to improve scroll behavior, ensuring smoother auto-scrolling when near the bottom of the chat.
- Refactored scroll logic to simplify conditions for showing and hiding the scroll-to-bottom button.
- Adjusted the `OptimizedList` widget to correctly handle item indexing based on the reverse property, enhancing list performance and usability.

lib/features/chat/widgets/assistant_message_widget.dart

@@ -18,7 +18,7 @@ import 'enhanced_attachment.dart';
 import 'package:conduit/shared/widgets/chat_action_button.dart';
 import '../../../shared/widgets/model_avatar.dart';
 import 'package:url_launcher/url_launcher_string.dart';
-import '../providers/chat_providers.dart' show sendMessage;
+import '../providers/chat_providers.dart' show sendMessageWithContainer;
 import '../../../core/utils/debug_logger.dart';
 import 'sources/openwebui_sources.dart';
 import '../providers/assistant_response_builder_provider.dart';
@@ -70,7 +70,8 @@ class _AssistantMessageWidgetState extends ConsumerState<AssistantMessageWidget>
       return;
     }
     try {
-      await sendMessage(ref, trimmed, null);
+      final container = ProviderScope.containerOf(context, listen: false);
+      await sendMessageWithContainer(container, trimmed, null);
     } catch (err, stack) {
       DebugLogger.log(
         'Failed to send follow-up: $err',