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.controller.ts

@@ -1,5 +1,5 @@
-import { Body, Controller, Post, Res, StreamableFile, UseGuards } from '@nestjs/common';
-import { ApiTags, ApiOperation, ApiBody } from '@nestjs/swagger';
+import { Body, Controller, Delete, Get, Param, Post, Query, Res, StreamableFile, UseGuards } from '@nestjs/common';
+import { ApiTags, ApiOperation, ApiBody, ApiQuery, ApiParam } from '@nestjs/swagger';
 import { Response } from 'express';
 import { JwtAuthGuard } from '../common/guards/jwt-auth.guard';
 import { CurrentUser } from '../common/decorators/current-user.decorator';
@@ -70,6 +70,37 @@ export class AiCoachController {
 
     return;
   }
+
+  @Get('conversations')
+  @ApiOperation({ summary: '获取会话列表' })
+  async listConversations(
+    @CurrentUser() user: AccessTokenPayload,
+    @Query() query: { page?: number, pageSize?: number },
+  ) {
+    return this.aiCoachService.listConversations(user.sub, { page: query.page, pageSize: query.pageSize });
+  }
+
+  @Get('conversations/:conversationId')
+  @ApiOperation({ summary: '获取会话详情（包含消息）' })
+  @ApiParam({ name: 'conversationId' })
+  async getConversationDetail(
+    @CurrentUser() user: AccessTokenPayload,
+    @Param('conversationId') conversationId: string,
+  ) {
+    const data = await this.aiCoachService.getConversationDetail(user.sub, conversationId);
+    return data || { code: 404, message: '会话不存在' };
+  }
+
+  @Delete('conversations/:conversationId')
+  @ApiOperation({ summary: '删除会话（级联删除消息）' })
+  @ApiParam({ name: 'conversationId' })
+  async deleteConversation(
+    @CurrentUser() user: AccessTokenPayload,
+    @Param('conversationId') conversationId: string,
+  ) {
+    const ok = await this.aiCoachService.deleteConversation(user.sub, conversationId);
+    return { success: ok };
+  }
 }