Add web dashboard, historical data loader, and backtest reporting

- Add Flask dashboard with status, config editor, logs, kill switch,
  and backtest results pages with monthly P&L breakdowns
- Add historical_loader.py for paginated OANDA candle fetching (1yr+)
- Update backtester to $100k starting equity, monthly P&L computation,
  and JSON summary output for dashboard display
- Update config to EUR_USD only on M5/M15 with SMA 21/50 strategy
- Add backtest.html template with performance metrics and bar charts

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

requirements.docker.txt

@@ -11,3 +11,5 @@ requests>=2.28
 supabase>=2.0
 python-dotenv>=1.0
 PyYAML>=6.0
+flask>=3.0
+flask-httpauth>=4.8