Add push notification functionality with tests and digest scheduler

- Implemented push subscription API with tests for subscribing and unsubscribing users.
- Created web push notification tests triggered by child actions.
- Added digest scheduler to send email digests to users at 9 PM local time.
- Developed utility functions for creating and validating digest action tokens.
- Integrated web push sender to handle sending notifications to users.
- Added service worker for handling push notifications in the frontend.
- Created a push opt-in component for user notification preferences.
- Implemented tests for the push opt-in component to ensure correct behavior.
- Updated frontend services to manage push subscriptions and permissions.

frontend/vue-app/src/layout/ParentLayout.vue

@@ -2,6 +2,7 @@
 import { useRouter, useRoute } from 'vue-router'
 import { computed, ref, onMounted, onUnmounted } from 'vue'
 import LoginButton from '../components/shared/LoginButton.vue'
+import PushOptIn from '../components/notification/PushOptIn.vue'
 import { eventBus } from '@/common/eventBus'
 import type {
   Event,
@@ -165,6 +166,7 @@ onUnmounted(() => {
     </header>
 
     <main class="main-content">
+      <PushOptIn />
       <router-view :key="$route.fullPath" />
     </main>