feat(kevin): reconcile Alpaca bracket auto-closes + order status

Bracket stop-loss/take-profit legs fill at Alpaca without passing through the executor, so those closes (and their P&L) were invisible locally.

- broker: add get_order(nested) + list_orders to BaseBroker/AlpacaBroker (+ SimulatedBroker); BrokerOrder carries child legs

- Trade gains broker_order_id (migration f6a7b8c9d0e1); executor stamps the entry order id

- new api_gateway trade-reconcile loop: books a closing SELL + realized P&L when a bracket leg fills (idempotent on the leg order id), syncs PENDING->terminal status, logs drift; runs alongside portfolio_sync

[ci skip]

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backtester/simulated_broker.py

@@ -13,6 +13,7 @@ from datetime import datetime, timezone
 from shared.broker.base import BaseBroker
 from shared.schemas.trading import (
     AccountInfo,
+    BrokerOrder,
     OrderRequest,
     OrderResult,
     OrderSide,
@@ -197,6 +198,27 @@ class SimulatedBroker(BaseBroker):
             timestamp=datetime.now(tz=timezone.utc),
         )
 
+    async def get_order(
+        self, order_id: str, *, nested: bool = True
+    ) -> BrokerOrder | None:
+        """Return a leg-less FILLED order — simulation has no bracket legs."""
+        return BrokerOrder(
+            order_id=order_id,
+            ticker="",
+            side=OrderSide.BUY,
+            qty=0,
+            filled_price=0.0,
+            status=OrderStatus.FILLED,
+            timestamp=datetime.now(tz=timezone.utc),
+            legs=[],
+        )
+
+    async def list_orders(
+        self, *, status: str = "all", limit: int = 100
+    ) -> list[OrderResult]:
+        """No standing-order book in simulation — return nothing."""
+        return []
+
     # ------------------------------------------------------------------
     # Extra backtest-only methods
     # ------------------------------------------------------------------