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/index.js

@@ -25,3 +25,19 @@ export const IndicatorRegistry = {
     stoch: StochasticIndicator,
     atr: ATRIndicator
 };
+
+/**
+ * Dynamically build the available indicators list from the registry.
+ * Each indicator class provides its own name and description via getMetadata().
+ */
+export function getAvailableIndicators() {
+    return Object.entries(IndicatorRegistry).map(([type, IndicatorClass]) => {
+        const instance = new IndicatorClass({ type, params: {}, name: '' });
+        const meta = instance.getMetadata();
+        return {
+            type,
+            name: meta.name || type.toUpperCase(),
+            description: meta.description || ''
+        };
+    });
+}