fix(kong): 修复contribution-service路由配置

- 将service URL从 /api/v2/contributions 改为根路径
- 设置 strip_path: false 直接透传请求路径
- 前端和后端现在都使用 /api/v2/contribution（单数）

前端请求: /api/v2/contribution/accounts/{id}
Kong转发: http://contribution-service:3020/api/v2/contribution/accounts/{id}

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

backend/api-gateway/kong.yml

@@ -277,18 +277,20 @@ services:
 
   # ---------------------------------------------------------------------------
   # Contribution Service 2.0 - 算力服务
+  # 前端路径: /api/v2/contribution/...
+  # 后端路径: /api/v2/contribution/... (strip_path: false, 直接透传)
   # ---------------------------------------------------------------------------
   - name: contribution-service-v2
-    url: http://192.168.1.111:3020/api/v2/contributions
+    url: http://192.168.1.111:3020
     routes:
       - name: contribution-v2-api
         paths:
           - /api/v2/contribution
-        strip_path: true
+        strip_path: false
       - name: contribution-v2-health
         paths:
           - /api/v2/contribution/health
-        strip_path: true
+        strip_path: false
 
   # ---------------------------------------------------------------------------
   # Mining Service 2.0 - 挖矿服务