fix(contribution-service): 修复控制器路由路径与前端API不匹配

将控制器路由从 /contributions 改为 /contribution，
与前端 api_endpoints.dart 中定义的路径保持一致。

完整路径: /api/v2/contribution/accounts/{accountSequence}

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

backend/services/contribution-service/src/api/controllers/contribution.controller.ts

@@ -13,7 +13,7 @@ import { ContributionRankingResponse, UserRankResponse } from '../dto/response/c
 import { GetContributionRecordsRequest } from '../dto/request/get-records.request';
 
 @ApiTags('Contribution')
-@Controller('contributions')
+@Controller('contribution')
 export class ContributionController {
   constructor(
     private readonly getAccountQuery: GetContributionAccountQuery,