feat(HEL-402): 接通网站首批只读 datahub 并建立双路对比

默认全部读取/影子开关关闭，网站继续走旧 Tushare 链路；开启单项时只替换该类原料并在失败时回旧，问天保持旧路径。

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

config/data-fields.config.json

@@ -2,6 +2,7 @@
   "schema_version": 1,
   "providers": {
     "tushare": {"class": "licensed", "calculation_allowed": true},
+    "datahub": {"class": "licensed", "calculation_allowed": true},
     "ifind": {"class": "licensed", "calculation_allowed": true},
     "eastmoney": {"class": "public_web", "calculation_allowed": false},
     "tencent": {"class": "public_web", "calculation_allowed": false},