Fix: restore tauriIpcAvailable definition in NavRail

ui/src/components/layout/NavRail.tsx

@@ -549,6 +549,7 @@ export const NavRail: React.FC<NavRailProps> = ({ className, mobile }) => {
   } | null>(null);
 
   const isDesktopApp = React.useMemo(() => isDesktopShell(), []);
+  const tauriIpcAvailable = React.useMemo(() => isTauriShell(), []);
 
   const formatLabel = React.useCallback(
     (project: ProjectEntry): string => {