feat(client): 新增会话管理与消息落库能力

补齐客户端会话生命周期接口（创建、列表、消息分页、改名、删除），并在流式 chat 中强制绑定 sessionId 与落库消息，确保会话标题和历史可追踪，同时统一 Swagger 文档为 DTO 驱动以减少重复维护。

Made-with: Cursor

src/apps/client-app/chat/chat.module.ts

@@ -1,13 +1,21 @@
 import { Module } from '@nestjs/common';
 import { ChatController } from './controllers/chat.controller';
+import { ChatSessionsController } from './controllers/chat-sessions.controller';
+import { ChatSessionService } from './application/chat-session.service';
 import { ProviderRouterService } from '@shared/ai-gateway/router/provider-router.service';
 import { QwenProvider } from '@shared/ai-gateway/providers/qwen.provider';
 import { DeepseekProvider } from '@shared/ai-gateway/providers/deepseek.provider';
 import { VolcProvider } from '@shared/ai-gateway/providers/volc.provider';
 
 @Module({
-  controllers: [ChatController],
-  providers: [ProviderRouterService, QwenProvider, DeepseekProvider, VolcProvider],
+  controllers: [ChatController, ChatSessionsController],
+  providers: [
+    ChatSessionService,
+    ProviderRouterService,
+    QwenProvider,
+    DeepseekProvider,
+    VolcProvider,
+  ],
 })
 export class ChatModule {}