feat: wire live decision loop and enable paper trading

Phase 2 of the autonomous trading engine:

- Replace start()/stop() stubs with real async implementations
- Decision loop: polls recommendations from PostgreSQL, deduplicates
  via Redis, evaluates through the full pipeline, submits orders to
  stonks:queue:broker_orders
- Stop-loss monitor: fetches prices from Polygon API, checks crossings,
  submits immediate sell orders, safety sell after 15 min without data
- Performance loop: computes metrics every 5 min during market hours,
  persists daily snapshots at market close
- Risk tier scheduler: evaluates daily at 16:00 ET, persists tier changes
- Rebalance scheduler: evaluates Monday 09:45 ET, respects circuit breaker
- Notification dispatch: SNS + Gmail with rate limiting and retry
- Backtest replay: fetches historical data, simulates decisions, persists
- Real asyncpg/redis connections in FastAPI lifespan (graceful degradation)
- Migration 019: enable paper trading with conservative tier, 5 cap
- Added max_open_positions to TradingConfig with env var loading
- Phase 2 tasks added to autonomous-trading-engine spec

infra/helm/stonks-oracle/values.yaml

@@ -208,6 +208,10 @@ config:
   ALERT_BROKER_ERROR_THRESHOLD: "3"
   ALERT_BROKER_ERROR_WINDOW_HOURS: "1"
   ALERT_CHECK_INTERVAL_SECONDS: "120"
+  TRADING_ENABLED: "true"
+  TRADING_RISK_TIER: "conservative"
+  TRADING_ABSOLUTE_POSITION_CAP: "25.0"
+  TRADING_MAX_OPEN_POSITIONS: "5"
 
 ## Secrets
 secrets: