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>

backend/bootstrap/settings.py

@@ -11,6 +11,8 @@ from backend.features.accounts.security import SecretVault
 def environment_credentials(environment: Mapping[str, str]) -> dict[str, str]:
     return {
         "tushare_token": str(environment.get("TUSHARE_TOKEN") or "").strip(),
+        "datahub_token": str(environment.get("DATAHUB_TOKEN") or "").strip(),
+        "datahub_base_url": str(environment.get("DATAHUB_BASE_URL") or "").strip(),
         "ifind_refresh_token": str(environment.get("IFIND_REFRESH_TOKEN") or "").strip(),
         "ifind_access_token": str(environment.get("IFIND_ACCESS_TOKEN") or "").strip(),
         "platform_llm_primary_api_key": str(