新增会话管理功能，包括获取会话列表、获取会话详情和删除会话的API，更新AI教练模块以支持会话模型，调整相关服务和数据传输对象。

src/ai-coach/ai-coach.module.ts

@@ -4,13 +4,14 @@ import { ConfigModule } from '@nestjs/config';
 import { AiCoachController } from './ai-coach.controller';
 import { AiCoachService } from './ai-coach.service';
 import { AiMessage } from './models/ai-message.model';
+import { AiConversation } from './models/ai-conversation.model';
 import { UsersModule } from '../users/users.module';
 
 @Module({
   imports: [
     ConfigModule,
     UsersModule,
-    SequelizeModule.forFeature([AiMessage]),
+    SequelizeModule.forFeature([AiConversation, AiMessage]),
   ],
   controllers: [AiCoachController],
   providers: [AiCoachService],