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/chat/data/services/ag_ui_service.dart

@@ -1,7 +1,7 @@
 import 'dart:async';
 import 'dart:convert';
 
-import 'package:social_app/core/config/env.dart';
+import 'package:social_app/core/api/i_api_client.dart';
 
 import '../ai/ai_decision_engine.dart';
 import '../models/ag_ui_event.dart';
@@ -24,27 +24,29 @@ const _textChunkSize = 10;
 typedef EventCallback = void Function(AgUiEvent event);
 
 class AgUiService {
+  final IApiClient? _apiClient;
   EventCallback onEvent;
   final AiDecisionEngine _decisionEngine;
   final MockHistoryService _historyService;
 
-  AgUiService({EventCallback? onEvent})
+  AgUiService({EventCallback? onEvent, IApiClient? apiClient})
     : onEvent = onEvent ?? ((_) {}),
+      _apiClient = apiClient,
       _decisionEngine = AiDecisionEngine(),
       _historyService = MockHistoryService();
 
   Future<void> sendMessage(String content) async {
-    if (Env.isMockApi) {
-      await _mockEventStream(content);
-    } else {
+    if (_apiClient != null) {
       throw UnimplementedError('Real API not implemented');
     }
+    await _mockEventStream(content);
   }
 
   Future<void> loadHistory({DateTime? beforeDate}) async {
-    if (Env.isMockApi) {
-      await _mockLoadHistory(beforeDate: beforeDate);
+    if (_apiClient != null) {
+      throw UnimplementedError('Real API not implemented');
     }
+    await _mockLoadHistory(beforeDate: beforeDate);
   }
 
   bool hasEarlierHistory(DateTime fromDate) {