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/market_data/config.py

@@ -0,0 +1,16 @@
+"""Configuration for the market data service."""
+
+from shared.config import BaseConfig
+
+
+class MarketDataConfig(BaseConfig):
+    """Extends BaseConfig with market-data-specific settings."""
+
+    watchlist: list[str] = ["AAPL", "TSLA", "NVDA", "MSFT", "GOOGL"]
+    bar_timeframe: str = "5Min"
+    poll_interval_seconds: int = 60
+    historical_bars: int = 100
+    alpaca_api_key: str = ""
+    alpaca_secret_key: str = ""
+
+    model_config = {"env_prefix": "TRADING_"}