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)

shared/schemas/trading.py

@@ -3,7 +3,7 @@
 from datetime import datetime
 from enum import Enum
 from typing import Any
-from uuid import UUID
+from uuid import UUID, uuid4
 
 from pydantic import BaseModel, Field
 
@@ -96,6 +96,7 @@ class AccountInfo(BaseModel):
 class TradeSignal(BaseModel):
     """Published to ``signals:generated`` by the signal generator."""
 
+    signal_id: UUID = Field(default_factory=uuid4)
     ticker: str
     direction: SignalDirection
     strength: float = Field(ge=0.0, le=1.0)