feat: update push notification subscription flow and remove deprecated opt-in component

frontend/vue-app/src/components/shared/LoginButton.vue

@@ -15,6 +15,7 @@ import {
 import { getCachedImageUrl, getCachedImageBlob } from '@/common/imageCache'
 import '@/assets/styles.css'
 import ModalDialog from './ModalDialog.vue'
+import { subscribeToPushWithResult } from '@/services/pushSubscription'
 
 const router = useRouter()
 const show = ref(false)
@@ -139,6 +140,7 @@ const submit = async () => {
     }
     // Authenticate parent and navigate
     authenticateParent(stayInParentMode.value)
+    subscribeToPushWithResult() // fire-and-forget — browser gesture is satisfied by the PIN button click
     close()
     const returnUrl = consumePendingReturnUrl()
     router.push(returnUrl || '/parent')