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>

tests/test_realtime_dashboard.py

@@ -133,6 +133,13 @@ class FakeFreeAggregator:
     def tencent_market_quotes(self, codes, expected_date=""):
         return self.eastmoney_market_quotes(expected_date)
 
+    def tencent_stock_quotes(self, codes, expected_date="", minimum=None):
+        wanted = {str(code).strip() for code in (codes or []) if str(code).strip()}
+        rows = self.tencent_market_quotes(codes, expected_date)
+        if not wanted:
+            return rows
+        return [row for row in rows if str(row.get("ts_code") or "") in wanted]
+
     def eastmoney_indices(self):
         return [
             {
@@ -318,6 +325,9 @@ class RealtimeDashboardTests(unittest.TestCase):
             def tencent_market_quotes(self, codes, expected_date=""):
                 return list(FREE_QUOTES)
 
+            def tencent_stock_quotes(self, codes, expected_date="", minimum=None):
+                return list(FREE_QUOTES)
+
         self.client.query = query
         self.client.realtime_aggregator = TencentOnlyAggregator()
         TushareClient._realtime_reference_cache.clear()