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/models/ai-message.model.ts

@@ -1,4 +1,5 @@
-import { Column, DataType, Index, Model, PrimaryKey, Table } from 'sequelize-typescript';
+import { BelongsTo, Column, DataType, ForeignKey, Model, PrimaryKey, Table } from 'sequelize-typescript';
+import { AiConversation } from './ai-conversation.model';
 
 export enum RoleType {
   System = 'system',
@@ -12,11 +13,11 @@ export enum RoleType {
 })
 export class AiMessage extends Model {
   @PrimaryKey
+  @ForeignKey(() => AiConversation)
   @Column({
     type: DataType.STRING,
     allowNull: false,
     comment: '会话ID',
-    primaryKey: true,
   })
   declare conversationId: string;
 
@@ -57,6 +58,9 @@ export class AiMessage extends Model {
     defaultValue: DataType.NOW,
   })
   declare updatedAt: Date;
+
+  @BelongsTo(() => AiConversation)
+  declare conversation?: AiConversation;
 }