feat: add backtesting functionality with UI and API endpoints

- Introduced backtesting page and fragment in the dashboard for running backtests and viewing recent reports.
- Implemented backtest run logic with configuration options including event path, starting balances, trade capital, and fee profiles.
- Added recent backtest reports storage and retrieval.
- Created a new strategy module for statistical arbitrage experiments with validation on configuration parameters.
- Updated settings to include parameters for the statistical arbitrage strategy.
- Enhanced dashboard controls to support the new strategy mode.
- Added unit tests for backtesting functionality and strategy validation.
- Updated templates for backtesting UI integration.

web/templates/dashboard.html

@@ -18,6 +18,7 @@ head_scripts %}
       >Refresh metrics</a
     >
     <a class="button secondary" href="/health">Health</a>
+    <a class="button secondary" href="/dashboard/backtesting">Backtesting</a>
   </div>
 </section>