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/indicators/stoch.js

@@ -31,6 +31,7 @@ export class StochasticIndicator extends BaseIndicator {
     getMetadata() {
         return {
             name: 'Stochastic',
+            description: 'Stochastic Oscillator - compares close to high-low range',
             inputs: [
                 { name: 'kPeriod', label: 'K Period', type: 'number', default: 14 },
                 { name: 'dPeriod', label: 'D Period', type: 'number', default: 3 }