fix: remove autocommit for named cursor in backtest

backend/backtest.py

@@ -348,7 +348,7 @@ def run_backtest(symbol: str, start_ms: int, end_ms: int, warmup_ms: int = WINDO
         host=PG_HOST, port=PG_PORT, dbname=PG_DB,
         user=PG_USER, password=PG_PASS
     )
-    conn.set_session(autocommit=True)
+    # named cursor需要在事务内（不要设autocommit=True）
 
     # 先warmup（用回测起点前4h的数据预热指标）
     warmup_start = start_ms - warmup_ms