feat(users): 添加用户语言偏好字段

- 在 User 模型中添加 language 字段，默认值为 'zh-CN'
- 更新 UpdateUserDto 以支持语言偏好参数
- 在用户更新服务中实现语言偏好的保存逻辑

src/users/dto/update-user.dto.ts

@@ -59,6 +59,11 @@ export class UpdateUserDto {
   @ApiProperty({ description: '活动水平（1-5的枚举值）', example: 3, minimum: 1, maximum: 5 })
   activityLevel?: number;
 
+  @IsString({ message: '语言偏好必须是字符串' })
+  @IsOptional()
+  @ApiProperty({ description: '用户语言偏好', example: 'zh-CN', required: false })
+  language?: string;
+
 }
 
 export class UpdateUserResponseDto {

src/users/models/user.model.ts

@@ -118,6 +118,14 @@ export class User extends Model {
   })
   declare deviceName: string;
 
+  @Column({
+    type: DataType.STRING,
+    allowNull: true,
+    defaultValue: 'zh-CN',
+    comment: '用户语言偏好（如：zh-CN、en-US）',
+  })
+  declare language: string;
+
   get isVip(): boolean {
     return this.membershipExpiration ? dayjs(this.membershipExpiration).isAfter(dayjs()) : false;
   }

src/users/users.service.ts

@@ -222,7 +222,7 @@ export class UsersService {
 
   // 更新用户昵称、头像
   async updateUser(updateUserDto: UpdateUserDto, userId: string): Promise<UpdateUserResponseDto> {
-    const { name, avatar, gender, birthDate, dailyStepsGoal, dailyCaloriesGoal, pilatesPurposes, weight, initialWeight, targetWeight, height, activityLevel } = updateUserDto;
+    const { name, avatar, gender, birthDate, language, dailyStepsGoal, dailyCaloriesGoal, pilatesPurposes, weight, initialWeight, targetWeight, height, activityLevel } = updateUserDto;
 
     this.logger.log(`updateUser: ${JSON.stringify(updateUserDto, null, 2)}`);
 
@@ -252,6 +252,10 @@ export class UsersService {
       user.birthDate = dayjs(birthDate * 1000).startOf('day').toDate();
       userChanges.birthDate = birthDate;
     }
+    if (language) {
+      user.language = language;
+      userChanges.language = language;
+    }
 
     this.logger.log(`updateUser user: ${JSON.stringify(user, null, 2)}`);