feat: Pattern Lab — historical backtest engine for pattern discovery

- Remove all built-in patterns (no proof of legitimacy); seed_builtin_patterns is now a no-op
- DB: add backtest_lab_runs table + backtest_hits/runs_count columns on patterns
- services/pattern_lab.py: build_historical_context (yfinance + RSI/MA200),
  run_ai_backtest (GPT-4o as historical analyst), evaluate_outcomes (actual moves at T+horizon)
- routers/pattern_lab.py: POST /run, POST /evaluate/{id}, GET /runs, DELETE /runs/{id},
  POST /save-pattern (promotes hit pattern to library with reliability counters)
- PatternLab.tsx: 34 preset events 2015-2025 (macro/geo/credit/fx/commodities/volatility/tech),
  3-panel layout — preset selector + wizard + run history, market data table,
  AI pattern cards with hit/miss outcome display, Save to Library button
- useApi.ts: usePatternLabRuns, useRunPatternLab, useEvaluatePatternLab, useSaveLabPattern, useDeleteLabRun
- Sidebar + App.tsx: /pattern-lab route + FlaskConical nav link

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/layout/Sidebar.tsx

@@ -13,6 +13,7 @@ const nav = [
   { to: '/macro', icon: Activity, label: 'Macro Regime' },
   { to: '/options', icon: TrendingUp, label: 'Options Lab' },
   { to: '/patterns', icon: Zap, label: 'Patterns' },
+  { to: '/pattern-lab', icon: FlaskConical, label: 'Pattern Lab' },
   { to: '/portfolio', icon: DollarSign, label: 'Portfolio' },
   { to: '/journal', icon: BookOpen, label: 'Trading Journal' },
   { to: '/rapport', icon: FileBarChart, label: 'Cycle Report' },