feat: add Daily Digest and Push Notifications toggles to User Profile with corresponding functionality

frontend/vue-app/src/services/pushSubscription.ts

@@ -172,3 +172,17 @@ export function getPushPermissionState(): NotificationPermission | 'unsupported'
   if (!('Notification' in window)) return 'unsupported'
   return Notification.permission
 }
+
+/**
+ * Returns true if the browser currently has an active push subscription.
+ */
+export async function isSubscribedToPush(): Promise<boolean> {
+  if (!('serviceWorker' in navigator) || !('PushManager' in window)) return false
+  try {
+    const registration = await navigator.serviceWorker.ready
+    const subscription = await registration.pushManager.getSubscription()
+    return subscription !== null
+  } catch {
+    return false
+  }
+}