Redesign indicators panel: dynamic catalog, multi-instance, chart legend

- Build indicator list dynamically from class getMetadata() instead of hardcoded array
- Remove checkboxes; single-click previews config, double-click adds to chart
- Support multiple instances of same indicator type (unique IDs)
- Add TradingView-style column legend overlay on chart (top-left)
- Recalculate indicators when historical data is prefetched on scroll
- Make indicator list and config panels scrollable (hidden scrollbars)
- Remove AVAILABLE_INDICATORS from strategies/config.js

src/api/dashboard/static/js/strategies/index.js

@@ -1,3 +1,3 @@
-export { StrategyParams, AVAILABLE_INDICATORS } from './config.js';
+export { StrategyParams } from './config.js';
 export { RiskManager } from './risk-manager.js';
 export { ClientStrategyEngine } from './engine.js';