fix(HEL-484): 中枢分时接口空 date 按当天查询

缺少或为空的 date 不再 400，按当天处理；显式历史日期保持原行为。

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

xiaobai-datahub/datahub/serving.py

@@ -269,8 +269,13 @@ class V1API:
         code = str(q.get("code") or "").strip()
         if not code:
             raise ApiError("INVALID_ARGUMENT", "code is required")
+        raw_date = str(q.get("date") or "").strip()
         try:
-            return fetch_intraday(self.db, code, yyyymmdd(q.get("date") or ""))
+            trade_date = yyyymmdd(raw_date or now_shanghai())
+        except ValueError as exc:
+            raise ApiError("INVALID_ARGUMENT", str(exc)) from exc
+        try:
+            return fetch_intraday(self.db, code, trade_date)
         except RealtimeApiError as exc:
             raise ApiError(exc.code, exc.message) from exc