feat: 添加好友功能并集成 LiteLLM 代理服务

- 新增好友搜索、添加、好友列表功能
- 集成 LiteLLM 代理服务及多模型定价配置
- 更新 iOS CocoaPods 配置
- 更新 .gitignore 和环境变量配置

apps/lib/core/di/injection.dart

@@ -11,6 +11,7 @@ import '../../features/auth/data/auth_repository.dart';
 import '../../features/auth/data/auth_repository_impl.dart';
 import '../../features/auth/presentation/bloc/auth_bloc.dart';
 import '../../features/calendar/ui/calendar_state_manager.dart';
+import '../../features/friends/data/friends_api.dart';
 import '../../features/users/data/users_api.dart';
 
 final sl = GetIt.instance;
@@ -44,6 +45,9 @@ Future<void> configureDependencies() async {
   final usersApi = UsersApi(apiClient);
   sl.registerSingleton<UsersApi>(usersApi);
 
+  final friendsApi = FriendsApi(apiClient);
+  sl.registerSingleton<FriendsApi>(friendsApi);
+
   final authRepository = AuthRepositoryImpl(
     api: authApi,
     tokenStorage: tokenStorage,