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.

public/sw.js

@@ -0,0 +1,126 @@
+// Custom service worker for push notifications
+// This will be merged with Workbox generated SW
+
+import { precacheAndRoute, cleanupOutdatedCaches } from 'workbox-precaching'
+import { clientsClaim, skipWaiting } from 'workbox-core'
+
+// Precache and route static assets
+precacheAndRoute(self.__WB_MANIFEST)
+cleanupOutdatedCaches()
+
+// Take control of all pages immediately
+skipWaiting()
+clientsClaim()
+
+// Push notification event handler
+self.addEventListener('push', (event) => {
+  console.log('Push event received:', event)
+  
+  let notificationData = {
+    title: 'New Announcement',
+    body: 'You have a new admin announcement',
+    icon: '/pwa-192x192.png',
+    badge: '/pwa-192x192.png',
+    data: {
+      url: '/',
+      timestamp: Date.now()
+    },
+    tag: 'admin-announcement',
+    requireInteraction: true,
+    actions: [
+      {
+        action: 'view',
+        title: 'View',
+        icon: '/pwa-192x192.png'
+      },
+      {
+        action: 'dismiss',
+        title: 'Dismiss'
+      }
+    ]
+  }
+
+  // Parse push data if available
+  if (event.data) {
+    try {
+      const pushData = event.data.json()
+      notificationData = {
+        ...notificationData,
+        ...pushData
+      }
+    } catch (error) {
+      console.warn('Failed to parse push data:', error)
+      // Use default notification data
+    }
+  }
+
+  event.waitUntil(
+    self.registration.showNotification(notificationData.title, notificationData)
+  )
+})
+
+// Notification click handler
+self.addEventListener('notificationclick', (event) => {
+  console.log('Notification clicked:', event)
+  
+  event.notification.close()
+
+  const action = event.action
+  const notificationData = event.notification.data || {}
+
+  if (action === 'dismiss') {
+    return // Just close the notification
+  }
+
+  // Default action or 'view' action - open the app
+  const urlToOpen = notificationData.url || '/'
+  
+  event.waitUntil(
+    clients.matchAll({ type: 'window', includeUncontrolled: true })
+      .then((clientList) => {
+        // Try to find an existing window with the app
+        for (const client of clientList) {
+          if (client.url.includes(self.location.origin) && 'focus' in client) {
+            client.focus()
+            // Navigate to the notification URL if different
+            if (client.url !== urlToOpen) {
+              client.navigate(urlToOpen)
+            }
+            return
+          }
+        }
+        // If no existing window, open a new one
+        if (clients.openWindow) {
+          return clients.openWindow(urlToOpen)
+        }
+      })
+  )
+})
+
+// Background sync for offline notification queue (future enhancement)
+self.addEventListener('sync', (event) => {
+  if (event.tag === 'notification-queue') {
+    event.waitUntil(
+      // Process any queued notifications when back online
+      console.log('Background sync: notification-queue')
+    )
+  }
+})
+
+// Message handler for communication with main app
+self.addEventListener('message', (event) => {
+  console.log('Service worker received message:', event.data)
+  
+  if (event.data && event.data.type === 'SHOW_NOTIFICATION') {
+    const { title, body, data } = event.data.payload
+    
+    self.registration.showNotification(title, {
+      body,
+      icon: '/pwa-192x192.png',
+      badge: '/pwa-192x192.png',
+      data,
+      tag: 'manual-notification',
+      requireInteraction: false
+    })
+  }
+})