feat(visualizer): add build overlay toggle

Default is off so candles match production; enable via the new Build button when needed.

apps/visualizer/src/features/chart/ChartToolbar.tsx

@@ -5,6 +5,8 @@ type Props = {
   onTimeframeChange: (tf: string) => void;
   showIndicators: boolean;
   onToggleIndicators: () => void;
+  showBuild: boolean;
+  onToggleBuild: () => void;
   priceAutoScale: boolean;
   onTogglePriceAutoScale: () => void;
   seriesLabel: string;
@@ -19,6 +21,8 @@ export default function ChartToolbar({
   onTimeframeChange,
   showIndicators,
   onToggleIndicators,
+  showBuild,
+  onToggleBuild,
   priceAutoScale,
   onTogglePriceAutoScale,
   seriesLabel,
@@ -45,6 +49,9 @@ export default function ChartToolbar({
         <Button size="sm" variant={showIndicators ? 'primary' : 'ghost'} onClick={onToggleIndicators} type="button">
           Indicators
         </Button>
+        <Button size="sm" variant={showBuild ? 'primary' : 'ghost'} onClick={onToggleBuild} type="button">
+          Build
+        </Button>
         <Button size="sm" variant={priceAutoScale ? 'primary' : 'ghost'} onClick={onTogglePriceAutoScale} type="button">
           Auto Scale
         </Button>