fix(leaderboard-service): add @IsIn validator to UpdateLeaderboardSwitchDto

The 'type' field was missing validation decorator, causing 400 Bad Request
when ValidationPipe with forbidNonWhitelisted was enabled.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/services/leaderboard-service/src/api/dto/leaderboard-config.dto.ts

@@ -1,5 +1,5 @@
 import { ApiProperty, ApiPropertyOptional } from '@nestjs/swagger';
-import { IsBoolean, IsInt, IsOptional, Min, Max } from 'class-validator';
+import { IsBoolean, IsInt, IsOptional, IsIn, Min, Max } from 'class-validator';
 import { Type } from 'class-transformer';
 
 /**
@@ -57,6 +57,7 @@ export class UpdateLeaderboardSwitchDto {
     description: '榜单类型',
     example: 'daily',
   })
+  @IsIn(['daily', 'weekly', 'monthly'])
   type: 'daily' | 'weekly' | 'monthly';
 
   @ApiProperty({ description: '是否启用', example: true })