fix(HEL-190): 按真实交易日历补齐最近60日快照，修复断档后只显示当天

保留连续性过滤，新增可审计补档工具与备份步骤；周末/节假日与真缺档分开处理，支持重复执行与部分失败续跑。

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

backend/features/market/repository.py

@@ -227,6 +227,31 @@ class MarketRepositoryMixin:
             result.append(payload)
         return result
 
+    def list_snapshot_trade_dates(
+        self,
+        start_date: str = "",
+        end_date: str = "",
+    ) -> list[str]:
+        clauses: list[str] = []
+        parameters: list[Any] = []
+        if start_date:
+            clauses.append("trade_date >= ?")
+            parameters.append(start_date)
+        if end_date:
+            clauses.append("trade_date <= ?")
+            parameters.append(end_date)
+        where = f"WHERE {' AND '.join(clauses)}" if clauses else ""
+        with self.connect() as connection:
+            rows = connection.execute(
+                f"""
+                SELECT trade_date FROM dashboard_snapshots
+                {where}
+                ORDER BY trade_date
+                """,
+                parameters,
+            ).fetchall()
+        return [str(row["trade_date"]) for row in rows]
+
     def start_sync(self, trade_date: str, source: str) -> int:
         started_at = datetime.now().astimezone().isoformat(timespec="seconds")
         with self.connect() as connection: