fix(settings): guard Notification API for iOS Safari

Notification is undefined on iOS Safari — bare access crashes on render.
Added "Notification" in window check before accessing .permission.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/(app)/settings/page.tsx

@@ -44,7 +44,7 @@ export default function SettingsPage() {
 
   const [thresholds, setThresholdsState] = useState(getThresholds);
   const [notifPermission, setNotifPermission] = useState<boolean>(
-    typeof window !== "undefined" && Notification.permission === "granted"
+    typeof window !== "undefined" && "Notification" in window && Notification.permission === "granted"
   );
 
   const [pushoverKey, setPushoverKey] = useState("");