fix(contribution): remove redundant snapshotDate from GetBatchRatiosRequest query DTO

The date is already read from URL path param @Param('date'), not query string.
Having it as required in the query DTO caused 400 Bad Request on ratios endpoint.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/services/contribution-service/src/api/dto/request/snapshot.request.ts

@@ -15,10 +15,6 @@ export class GetSnapshotRequest {
 }
 
 export class GetBatchRatiosRequest {
-  @ApiProperty({ description: '快照日期 (YYYY-MM-DD)' })
-  @IsDateString()
-  snapshotDate: string;
-
   @ApiPropertyOptional({ description: '页码', default: 1 })
   @IsOptional()
   @Type(() => Number)