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>

src/order_executor.py

@@ -465,6 +465,18 @@ if __name__ == "__main__":
         print(f"Running on {interval}s loop. Press Ctrl+C to stop.\n")
         while True:
             try:
+                # Check for config reload signal from dashboard
+                reload_signal = get_project_root() / "RELOAD_CONFIG"
+                if reload_signal.exists():
+                    print("\n*** CONFIG RELOAD REQUESTED ***")
+                    try:
+                        reload_signal.unlink()
+                    except OSError:
+                        pass
+                    cfg = load_config()
+                    interval = cfg.get("execution", {}).get("interval_seconds", 60)
+                    print(f"Config reloaded. Interval now {interval}s.\n")
+
                 main()
                 print(f"\nSleeping {interval}s until next run...\n")
                 time.sleep(interval)