refactor(apps): simplify API layer by removing redundant wrapper classes

- Remove ApiClientWrapper and MockApiClientWrapper
- Simplify IApiClient interface
- Update dependency injection configuration
- Optimize calendar service and AG-UI chat models

apps/lib/features/auth/data/auth_api.dart

@@ -1,10 +1,10 @@
-import 'package:social_app/core/api/api_client.dart';
+import 'package:social_app/core/api/i_api_client.dart';
 import 'models/signup_request.dart';
 import 'models/login_request.dart';
 import 'models/auth_response.dart';
 
 class AuthApi {
-  final ApiClient _client;
+  final IApiClient _client;
   static const _prefix = '/api/v1/auth';
 
   AuthApi(this._client);