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/config.py

@@ -16,6 +16,12 @@ class ApiGatewayConfig(BaseConfig):
     access_token_expire_minutes: int = 15
     refresh_token_expire_days: int = 7
 
+    # Alpaca brokerage credentials (for portfolio sync)
+    alpaca_api_key: str = ""
+    alpaca_secret_key: str = ""
+    paper_trading: bool = True
+    snapshot_interval_seconds: int = 60
+
     # CORS settings
     cors_origins: list[str] = ["http://localhost:5173"]