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/api_gateway/main.py

@@ -46,20 +46,26 @@ def create_app(config: ApiGatewayConfig | None = None) -> FastAPI:
 
         # Start portfolio sync background task
         from services.api_gateway.tasks.portfolio_sync import portfolio_sync_loop
+        from services.api_gateway.tasks.trade_reconcile import trade_reconcile_loop
 
         sync_task = asyncio.create_task(
             portfolio_sync_loop(config, session_factory)
         )
+        reconcile_task = asyncio.create_task(
+            trade_reconcile_loop(config, session_factory)
+        )
 
         logger.info("API Gateway started")
         yield
 
-        # Cancel the sync task
+        # Cancel the background tasks
         sync_task.cancel()
-        try:
-            await sync_task
-        except asyncio.CancelledError:
-            pass
+        reconcile_task.cancel()
+        for task in (sync_task, reconcile_task):
+            try:
+                await task
+            except asyncio.CancelledError:
+                pass
 
         # Cleanup
         await app.state.redis.aclose()