[FEATURE] Implement backtest controls in visualization dashboard

[chizy7]

Description

The visualization dashboard has placeholder implementations for backtest functionality that need to be connected to the backend backtest engine.

Current Behavior

Location: visualization/static/app.js:691-700

runBacktest() {
    // Placeholder for backtest functionality
    console.log('Running backtest...');
    // In a real implementation, this would send a request to start a backtest
}

refreshBacktests() {
    // Placeholder for refreshing backtest results
    console.log('Refreshing backtests...');
    // In a real implementation, this would fetch latest backtest results
}

• Buttons exist in UI but do nothing
• No backend API integration
• No backtest results displayed

Expected Behavior

runBacktest()

• Send POST request to /api/v1/backtests with configuration
• Display loading indicator
• Show progress updates via WebSocket
• Display results when complete

refreshBacktests()

• Send GET request to /api/v1/backtests
• Update backtest results table
• Show latest backtest status and metrics

Implementation Requirements

1. Add REST API endpoints for backtest management
2. Implement WebSocket progress updates
3. Connect to existing BacktestEngine (already exists in codebase)
4. Display results in dashboard UI

Affected Files

• visualization/static/app.js
• visualization/WebServer.cpp (add endpoints)
• visualization/static/index.html (results display)