feat(execution): AccountOrderWorker로 매수·매도 주문 직렬화

전략별 tick/scan 매도 락 대신 계좌 단일 PriorityQueue로 place를 B-full 직렬화한다.
틱매도 only_code 필터와 inflight 중복 enqueue 방지로 REST 폭주를 줄인다.

Co-authored-by: Cursor <cursoragent@cursor.com>

kis_trader/strategies/scalping.py

@@ -331,7 +331,7 @@ class ScalpingStrategy(BaseStrategy):
     # ------------------------------------------------------------------
     # 매도
     # ------------------------------------------------------------------
-    def check_sell_signals(self) -> List[Dict]:
+    def check_sell_signals(self, only_code: Optional[str] = None) -> List[Dict]:
         """엔진 check_sell_signal_live 사용 (백테스트 동일)."""
         if not self.holdings:
             return []
@@ -348,7 +348,11 @@ class ScalpingStrategy(BaseStrategy):
         )
 
         try:
-            params = se.get_scalping_defaults_from_db()
+            cached = getattr(self, "_scan_engine_params", None) or {}
+            if cached:
+                params = dict(cached)
+            else:
+                params = se.get_scalping_defaults_from_db()
         except Exception:
             params = {}
         params.update({
@@ -370,6 +374,8 @@ class ScalpingStrategy(BaseStrategy):
         })
 
         for code, holding in list(self.holdings.items()):
+            if only_code and code != only_code:
+                continue
             try:
                 name = holding.get("name", code)
                 buy_price = float(holding.get("buy_price", 0))