fix: stabilize presenter route loading

web/apps/console/src/app/AppRoutes.tsx

@@ -7,12 +7,18 @@ const PresenterRoute = lazy(() => import("../presentation/presenter/PresenterRou
   default: module.PresenterRoute,
 })));
 
+const PresenterRouteFallback = () => (
+  <main className="presenter-route" aria-label="Presenter notes loading" aria-busy="true">
+    <p>Loading presenter notes...</p>
+  </main>
+);
+
 export const AppRoutes = () => (
   <Routes>
     <Route path="/" element={<ConsoleHome />} />
     <Route path="/console" element={<ConsoleHome />} />
     <Route path="/present" element={<PresentationRoute />} />
-    <Route path="/presenter" element={<Suspense fallback={null}><PresenterRoute /></Suspense>} />
+    <Route path="/presenter" element={<Suspense fallback={<PresenterRouteFallback />}><PresenterRoute /></Suspense>} />
     <Route path="*" element={<Navigate to="/" replace />} />
   </Routes>
 );