fix(HEL-494): 盘中双免费源故障切换并禁止问天假0覆盖

主源东财失败后自动改走腾讯行情，成功结果写入缓存；两源都失败时返回最近真实快照并标明延迟，不再显示假0。

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

backend/data/datahub/bridge.py

@@ -240,9 +240,17 @@ class DatahubBridge:
                     rows = dated
             if len(rows) < minimum:
                 raise DatahubError("EMPTY", f"datahub {dataset} empty")
-            if (response.meta or {}).get("stale"):
-                raise DatahubError("STALE", f"datahub {dataset} stale")
-            self._record_route(dataset, "datahub", str((response.meta or {}).get("source") or "datahub"))
+            stale = bool((response.meta or {}).get("stale"))
+            delay = int((response.meta or {}).get("staleness_seconds") or 0)
+            notice = str((response.meta or {}).get("delay_notice") or "")
+            source = str((response.meta or {}).get("source") or "datahub")
+            if stale:
+                for item in rows:
+                    item["delayed"] = True
+                    item["delay_seconds"] = delay
+                    item["delay_notice"] = notice
+                    item["source"] = source
+            self._record_route(dataset, "datahub", source)
             return rows
         except Exception as exc:
             self._log_failure(dataset, exc)
@@ -444,7 +452,7 @@ def _native_quote(row: dict[str, Any]) -> dict[str, Any] | None:
     if not ts_code or close <= 0 or previous <= 0:
         return None
     volume = _finite(row.get("vol") if row.get("vol") not in (None, "") else row.get("volume"))
-    return {
+    payload = {
         "ts_code": ts_code,
         "name": str(row.get("name") or ts_code).strip(),
         "pre_close": previous,
@@ -458,6 +466,11 @@ def _native_quote(row: dict[str, Any]) -> dict[str, Any] | None:
         "quote_date": yyyymmdd(row.get("quote_date") or row.get("trade_date")),
         "source": str(row.get("source") or "datahub"),
     }
+    if row.get("delayed"):
+        payload["delayed"] = True
+        payload["delay_seconds"] = int(row.get("delay_seconds") or 0)
+        payload["delay_notice"] = str(row.get("delay_notice") or "")
+    return payload
 
 
 def _chart_bars(rows: list[Any]) -> list[dict[str, Any]]: