fix(HEL-494): 网站市场客户端改为纯中枢 Facade，并迁移 iFinD 凭据到中枢

生产 gateway 不再读取 Tushare token 或实例化 TushareProvider/TushareClient；问财凭据经带鉴权的中枢接口加密入库，避免发版后 iFinD 未配置。

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: multica-agent <github@multica.ai>

backend/data/datahub/client.py

@@ -96,6 +96,15 @@ class DatahubClient:
             {"api_name": api_name, "params": params or {}, "fields": fields},
         )
 
+    def put_ifind_credentials(self, refresh_token: str, access_token: str = "") -> DatahubResponse:
+        return self.post(
+            "/v1/credentials/ifind",
+            {
+                "ifind_refresh_token": refresh_token,
+                "ifind_access_token": access_token,
+            },
+        )
+
     def sector_quote(self, code: str, date: str = "") -> DatahubResponse:
         payload: dict[str, Any] = {"code": code}
         if date: