fix(HEL-494): 数据中枢独占调度，主网站不再回退旧接口

主网站只向中枢要业务数据；来源选择、切源、补数全部在中枢内部完成，失败不再走东财/腾讯/Tushare 保底。

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

backend/data/providers/tushare_daily.py

@@ -186,12 +186,11 @@ class DailyMarketMixin:
         return mapped
 
     def _free_board_map(self, trade_date: str) -> dict[str, dict[str, Any]]:
-        aggregator = getattr(self, "realtime_aggregator", None)
-        loader = getattr(aggregator, "eastmoney_limit_pool", None) if aggregator else None
+        loader = getattr(self, "try_limit_pool", None)
         if not callable(loader):
             return {}
         try:
-            rows = loader(trade_date)
+            rows = loader(trade_date) or []
         except Exception:
             return {}
         return {