feat(ai-coach,checkins): 实现软删除功能

在AI教练和打卡模块中添加deleted字段，将物理删除改为软删除：
- 在AiConversation和AiMessage模型中添加deleted布尔字段
- 在Checkin模型中添加deleted字段
- 更新所有查询条件添加deleted: false过滤
- 修改删除操作为标记deleted: true而非物理删除
- 在打卡服务中添加重复记录检查逻辑

src/checkins/checkins.service.ts

@@ -19,6 +19,21 @@ export class CheckinsService {
   ) { }
 
   async create(dto: CreateCheckinDto): Promise<CheckinResponseDto> {
+    // 检查是否已存在未删除的记录
+    const existingRecord = await this.checkinModel.findOne({
+      where: {
+        userId: dto.userId,
+        workoutId: dto.workoutId || null,
+        planId: dto.planId || null,
+        checkinDate: dto.checkinDate || null,
+        deleted: false,
+      },
+    });
+
+    if (existingRecord) {
+      return { code: ResponseCode.SUCCESS, message: 'success', data: existingRecord.toJSON() };
+    }
+
     const record = await this.checkinModel.create({
       userId: dto.userId,
       workoutId: dto.workoutId || null,
@@ -43,7 +58,12 @@ export class CheckinsService {
   }
 
   async update(dto: UpdateCheckinDto, userId: string): Promise<CheckinResponseDto> {
-    const record = await this.checkinModel.findByPk(dto.id);
+    const record = await this.checkinModel.findOne({
+      where: {
+        id: dto.id,
+        deleted: false,
+      },
+    });
     if (!record) {
       throw new NotFoundException('打卡记录不存在');
     }
@@ -75,7 +95,12 @@ export class CheckinsService {
   }
 
   async complete(dto: CompleteCheckinDto, userId: string): Promise<CheckinResponseDto> {
-    const record = await this.checkinModel.findByPk(dto.id);
+    const record = await this.checkinModel.findOne({
+      where: {
+        id: dto.id,
+        deleted: false,
+      },
+    });
     if (!record) {
       throw new NotFoundException('打卡记录不存在');
     }
@@ -114,7 +139,8 @@ export class CheckinsService {
     if (record.userId !== userId) {
       throw new ForbiddenException('无权操作该打卡记录');
     }
-    await record.destroy();
+    record.deleted = true;
+    await record.save();
     await this.activityLogsService.record({
       userId: record.userId,
       entityType: ActivityEntityType.CHECKIN,
@@ -139,6 +165,7 @@ export class CheckinsService {
     const rows = await this.checkinModel.findAll({
       where: {
         userId,
+        deleted: false,
         [Op.or]: [
           { checkinDate: target.format('YYYY-MM-DD') as any },
           {
@@ -170,6 +197,7 @@ export class CheckinsService {
     const rows = await this.checkinModel.findAll({
       where: {
         userId,
+        deleted: false,
         [Op.or]: [
           {
             checkinDate: {