Add trade setup outcome tracking and performance stats

Closes the feedback loop on R:R scanner signals:

- Nightly outcome_evaluator job replays unresolved setups against daily
  OHLCV bars: target_hit / stop_hit / ambiguous (same-bar, counted as
  loss) / expired after OUTCOME_EVALUATION_MAX_BARS (default 30)
- Migration 004: evaluated_at + outcome_date on trade_setups
- GET /trades/performance: hit rate, expectancy (avg R), total R with
  breakdowns by direction, recommended action, and confidence bucket
- New Performance page (stat cards, breakdown tables, Evaluate Now,
  methodology disclosure) wired into sidebar and mobile nav
- 17 new unit tests for evaluation logic and stats aggregation

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/components/layout/MobileNav.tsx

@@ -6,6 +6,7 @@ const navItems = [
   { to: '/watchlist', label: 'Watchlist' },
   { to: '/scanner', label: 'Scanner' },
   { to: '/rankings', label: 'Rankings' },
+  { to: '/performance', label: 'Performance' },
 ];
 
 export default function MobileNav() {