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)

docker-compose.yml

@@ -142,6 +142,19 @@ services:
     env_file: .env
     restart: unless-stopped
 
+  market-data:
+    build:
+      context: .
+      dockerfile: docker/Dockerfile.service
+      args:
+        EXTRAS: "trading"
+        SERVICE_MODULE: "market_data"
+    depends_on:
+      redis:
+        condition: service_healthy
+    env_file: .env
+    restart: unless-stopped
+
   api-gateway:
     build:
       context: .