fix: Add default export to DashboardPage to fix lazy loading

The React.lazy import was expecting a default export, but the
component was only exported as a named export (NewDashboardPage).
This caused the error: "can't convert item to string"

Added default export while keeping the named export for compatibility.

frontend/src/pages/app/DashboardPage.tsx

@@ -231,3 +231,5 @@ export function NewDashboardPage() {
     </div>
   );
 }
+
+export default NewDashboardPage;