feat(visualizer): add build overlay toggle

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

apps/visualizer/src/App.tsx

@@ -107,6 +107,7 @@ function TradeApp({ user, onLogout }: { user: string; onLogout: () => void }) {
   const [pollMs, setPollMs] = useLocalStorageState('trade.pollMs', envNumber('VITE_POLL_MS', 1000));
   const [limit, setLimit] = useLocalStorageState('trade.limit', envNumber('VITE_LIMIT', 300));
   const [showIndicators, setShowIndicators] = useLocalStorageState('trade.showIndicators', true);
+  const [showBuild, setShowBuild] = useLocalStorageState('trade.showBuild', false);
   const [tab, setTab] = useLocalStorageState<'orderbook' | 'trades'>('trade.sidebarTab', 'orderbook');
   const [bottomTab, setBottomTab] = useLocalStorageState<
     'positions' | 'orders' | 'balances' | 'orderHistory' | 'positionHistory'
@@ -288,6 +289,8 @@ function TradeApp({ user, onLogout }: { user: string; onLogout: () => void }) {
             onTimeframeChange={setTf}
             showIndicators={showIndicators}
             onToggleIndicators={() => setShowIndicators((v) => !v)}
+            showBuild={showBuild}
+            onToggleBuild={() => setShowBuild((v) => !v)}
             seriesLabel={seriesLabel}
           />