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/api/chat_api.dart

@@ -6,6 +6,18 @@ import '../models/conversation.dart';
 import '../models/message.dart';
 import 'api_client.dart';
 
+sealed class ChatStreamEvent {}
+
+class ChatTextChunk extends ChatStreamEvent {
+  final String text;
+  ChatTextChunk(this.text);
+}
+
+class ChatStatusUpdate extends ChatStreamEvent {
+  final String status; // empty string = clear status
+  ChatStatusUpdate(this.status);
+}
+
 class ChatApi {
   final Dio _dio;
   const ChatApi(this._dio);
@@ -71,8 +83,8 @@ class ChatApi {
     }
   }
 
-  // Step 2: GET the SSE stream and yield text chunks.
-  Stream<String> streamGeneration(int conversationId) async* {
+  // Step 2: GET the SSE stream and yield typed events (text chunks + status updates).
+  Stream<ChatStreamEvent> streamGeneration(int conversationId) async* {
     try {
       final response = await _dio.get(
         '/api/chat/conversations/$conversationId/generation/stream',
@@ -108,14 +120,21 @@ class ChatApi {
             if (data == '[DONE]') return;
             if (currentEvent == 'done' || currentEvent == 'error') return;
 
-            // Parse as JSON if possible, otherwise yield raw text.
             if (currentEvent == 'chunk' || currentEvent.isEmpty) {
               try {
                 final obj = json.decode(data) as Map<String, dynamic>;
                 final text = obj['text'] as String? ?? '';
-                if (text.isNotEmpty) yield text;
+                if (text.isNotEmpty) yield ChatTextChunk(text);
               } catch (_) {
-                if (data.isNotEmpty) yield data;
+                if (data.isNotEmpty) yield ChatTextChunk(data);
+              }
+            } else if (currentEvent == 'status') {
+              try {
+                final obj = json.decode(data) as Map<String, dynamic>;
+                final status = obj['status'] as String? ?? '';
+                yield ChatStatusUpdate(status);
+              } catch (_) {
+                // Ignore malformed status events
               }
             }
           } else if (line.isEmpty) {