feat: Implement push notification system for admin announcements

- Add a notification manager to handle push notifications and integrate with Nostr events.
- Create a push notification service to manage subscription and permission requests.
- Introduce components for notification settings and permission prompts in the UI.
- Update Nostr store to manage push notification state and enable/disable functionality.
- Enhance NostrFeed to send notifications for new admin announcements.
- Implement test notification functionality for development purposes.

src/pages/Home.vue

@@ -1,9 +1,11 @@
 <template>
-  <div class="container py-8">
+  <div class="container py-8 space-y-6">
+    <NotificationPermission auto-show />
     <NostrFeed feed-type="announcements" />
   </div>
 </template>
 
 <script setup lang="ts">
 import NostrFeed from '@/components/nostr/NostrFeed.vue'
+import NotificationPermission from '@/components/notifications/NotificationPermission.vue'
 </script>