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>

services/trade_executor/main.py

@@ -256,6 +256,7 @@ async def process_signal(
                     strategy_id=signal.strategy_id,
                     status=status_map.get(result.status, TradeStatusModel.PENDING),
                     pnl=realized_pnl,
+                    broker_order_id=result.order_id or None,
                 )
                 session.add(db_trade)
                 await session.commit()