feat: 更新AI教练控制器，增加用户聊天次数管理功能

- 在AI教练控制器中引入用户聊天次数的检查，确保用户在进行对话前有足够的聊天次数。
- 新增用户服务方法以获取和扣减用户的聊天次数，优化用户体验。
- 调整默认免费聊天次数为5次，提升系统的使用限制管理。

src/users/users.service.ts

@@ -36,7 +36,7 @@ import { ActivityLogsService } from '../activity-logs/activity-logs.service';
 import { ActivityActionType, ActivityEntityType } from '../activity-logs/models/activity-log.model';
 import { CreateDietRecordDto, UpdateDietRecordDto, GetDietHistoryQueryDto, DietRecordResponseDto, DietHistoryResponseDto, NutritionSummaryDto } from './dto/diet-record.dto';
 
-const DEFAULT_FREE_USAGE_COUNT = 10;
+const DEFAULT_FREE_USAGE_COUNT = 5;
 
 @Injectable()
 export class UsersService {
@@ -126,6 +126,49 @@ export class UsersService {
     }
   }
 
+  /**
+   * @desc 获取用户剩余的聊天次数
+   */
+  async getUserUsageCount(userId: string): Promise<number> {
+    try {
+      const user = await this.userModel.findOne({ where: { id: userId } });
+
+      if (!user) {
+        this.logger.log(`getUserUsageCount: ${userId} not found, return 0`);
+        return 0
+      }
+
+      if (user.isVip) {
+        // 会员用户无限次
+        this.logger.log(`getUserUsageCount: ${userId} is vip, return 999`);
+        return 999
+      }
+
+      this.logger.log(`getUserUsageCount: ${userId} freeUsageCount: ${user.freeUsageCount}`);
+
+      return user.freeUsageCount || 0;
+    } catch (error) {
+      this.logger.error(`getUserUsageCount error: ${error instanceof Error ? error.message : String(error)}`);
+      return 0
+    }
+  }
+
+  // 扣减用户免费次数
+  async deductUserUsageCount(userId: string, count: number = 1): Promise<void> {
+    try {
+      this.logger.log(`deductUserUsageCount: ${userId} deduct ${count} times`);
+      const user = await this.userModel.findOne({ where: { id: userId } });
+      if (!user) {
+        throw new NotFoundException(`ID为${userId}的用户不存在`);
+      }
+      user.freeUsageCount -= count;
+      await user.save();
+    } catch (error) {
+      this.logger.error(`deductUserUsageCount error: ${error instanceof Error ? error.message : String(error)}`);
+      throw error;
+    }
+  }
+
 
   // 更新用户昵称、头像
   async updateUser(updateUserDto: UpdateUserDto): Promise<UpdateUserResponseDto> {
@@ -453,8 +496,8 @@ export class UsersService {
   }
 
   /**
-   * 获取最近N顿饮食的营养汇总
-   */
+ * 获取最近N顿饮食的营养汇总
+ */
   async getRecentNutritionSummary(userId: string, mealCount: number = 10): Promise<NutritionSummaryDto> {
     const records = await this.userDietHistoryModel.findAll({
       where: { userId, deleted: false },