fix(menu): update parentId example to a string format

apps/box-mgnt-api/src/mgnt-backend/core/menu/menu.dto.ts

@@ -17,7 +17,7 @@ import { ApiProperty, ApiPropertyOptional } from '@nestjs/swagger';
 export class MenuDto {
   @ApiPropertyOptional({
     description: '父菜单 ID，若为顶级菜单则为空',
-    example: 0,
+    example: 'xxxxx',
   })
   @IsString()
   @IsOptional()