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>

config/architecture-inventory.json

@@ -636,16 +636,16 @@
       "bytes": 8357,
       "lines": 116
     },
+    {
+      "path": "backend/application.py",
+      "bytes": 6997,
+      "lines": 182
+    },
     {
       "path": "backend/features/screener/formula.py",
       "bytes": 6983,
       "lines": 146
     },
-    {
-      "path": "backend/application.py",
-      "bytes": 6751,
-      "lines": 178
-    },
     {
       "path": "backend/features/market/insights_popularity.py",
       "bytes": 6739,