feat: show tool status notifications in chat during generation

Parse SSE `status` events alongside `chunk` events and display the
status text next to the spinner while the assistant is generating.
Previously the Android app discarded all non-chunk SSE events.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/data/repositories/chat_repository.dart

@@ -1,4 +1,5 @@
 import '../api/chat_api.dart';
+export '../api/chat_api.dart' show ChatStreamEvent, ChatTextChunk, ChatStatusUpdate;
 import '../models/conversation.dart';
 import '../models/message.dart';
 
@@ -14,6 +15,6 @@ class ChatRepository {
       _api.getMessages(conversationId);
   Future<void> sendMessage(int conversationId, String content) =>
       _api.sendMessage(conversationId, content);
-  Stream<String> streamGeneration(int conversationId) =>
+  Stream<ChatStreamEvent> streamGeneration(int conversationId) =>
       _api.streamGeneration(conversationId);
 }