feat: real data pipeline — market data, DB persistence, portfolio sync, signal-trade linkage

Wire the trading bot to real Alpaca market data and persist pipeline
state to the database so the dashboard displays live information.

- Add market-data service fetching OHLCV bars from Alpaca, publishing
  to market:bars Redis Stream; signal generator consumes bars and
  injects current_price into signals for position sizing
- Sentiment analyzer now persists Article + ArticleSentiment rows to
  DB after scoring, with duplicate and error handling
- API gateway runs a background portfolio sync task that snapshots
  Alpaca account state into PortfolioSnapshot/Position DB tables
  during market hours
- TradeSignal carries a signal_id UUID; signal generator and trade
  executor both persist their records to DB with cross-references
- 303 unit tests pass (57 new tests added)

services/api_gateway/main.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import asyncio
 import logging
 from contextlib import asynccontextmanager
 from typing import AsyncIterator
@@ -43,9 +44,23 @@ def create_app(config: ApiGatewayConfig | None = None) -> FastAPI:
         )
         app.state.config = config
 
+        # Start portfolio sync background task
+        from services.api_gateway.tasks.portfolio_sync import portfolio_sync_loop
+
+        sync_task = asyncio.create_task(
+            portfolio_sync_loop(config, session_factory)
+        )
+
         logger.info("API Gateway started")
         yield
 
+        # Cancel the sync task
+        sync_task.cancel()
+        try:
+            await sync_task
+        except asyncio.CancelledError:
+            pass
+
         # Cleanup
         await app.state.redis.aclose()
         await engine.dispose()