feat: 增强 HomeScreen 录音交互与 ChatBloc 状态管理

- 新增录音启动延迟处理，解决权限未就绪时的竞态问题
- 实现历史分页滚动位置保持，提升加载体验
- 添加文本输入框点击键盘显示与焦点管理
- 优化 ChatBloc provider 到 MultiBlocProvider 支持
- 修复 ApiException 429 错误详情解析（支持 JSON 字符串 body）
- 改进 LocalNotificationService 精确闹钟权限请求
- 优化 UiSchemaRenderer GridView children 生成
- 支持导航 action 的 replace 参数
- 移除 Agent router 速率限制逻辑（_allow_run_request, _allow_transcribe_request）
- 补充相关单元测试与集成测试

apps/test/core/api/api_exception_test.dart

@@ -1,4 +1,5 @@
 import 'package:flutter_test/flutter_test.dart';
+import 'package:dio/dio.dart';
 import 'package:social_app/core/api/api_exception.dart';
 
 void main() {
@@ -15,5 +16,37 @@ void main() {
       const exception = UnauthorizedException();
       expect(exception.message, '请重新登录');
     });
+
+    test('429 returns backend detail message', () {
+      final dioException = DioException(
+        requestOptions: RequestOptions(path: '/api/v1/agent/runs'),
+        response: Response<dynamic>(
+          requestOptions: RequestOptions(path: '/api/v1/agent/runs'),
+          statusCode: 429,
+          data: <String, dynamic>{'detail': 'Too many SSE connections'},
+        ),
+      );
+
+      final apiException = ApiException.fromDioError(dioException);
+
+      expect(apiException.statusCode, 429);
+      expect(apiException.message, 'Too many SSE connections');
+    });
+
+    test('429 parses detail from string json body', () {
+      final dioException = DioException(
+        requestOptions: RequestOptions(path: '/api/v1/agent/runs'),
+        response: Response<dynamic>(
+          requestOptions: RequestOptions(path: '/api/v1/agent/runs'),
+          statusCode: 429,
+          data: '{"detail":"Too many SSE connections"}',
+        ),
+      );
+
+      final apiException = ApiException.fromDioError(dioException);
+
+      expect(apiException.statusCode, 429);
+      expect(apiException.message, 'Too many SSE connections');
+    });
   });
 }