fix: update notification icon handling to use default avatar if unavailable

src/app/pages/client/ClientNonUIFeatures.tsx

@@ -243,9 +243,10 @@ function MessageNotifications() {
         // Use renderer window.Notification — works in both Electron and browser.
         // Main-process Notification click events are unreliable on Windows without
         // full COM/AUMID registration, so we keep everything in the renderer.
+        const iconUrl = roomAvatar ?? '/res/android/android-chrome-192x192.png';
+
         const noti = new window.Notification(notificationTitle, {
-          icon: roomAvatar,
-          badge: roomAvatar,
+          icon: iconUrl,
           body: notificationBody,
           silent: true,
         });