Add background notifications and fix Discord/Slack notification bugs

Background Notification Features:
- Implement Web Push Notifications for alerts when browser is minimized
- Add Service Worker for persistent background notification support
- Integrate Page Visibility API to detect when page is in background
- Add browser notification permission request with user consent flow
- Create more aggressive background polling (10 seconds) when page hidden
- Add vibration patterns for mobile device alerts

Bug Fixes:
- Fix Discord/Slack notification parameter order bug preventing delivery
- Add comprehensive logging for notification debugging
- Correct webhook function signatures for proper data passing

Mobile Enhancements:
- Support system notifications on Android browsers
- Add click-to-focus functionality for notifications
- Implement background alert system for multitasking
- Add notification button with visual feedback

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

assets/js/twp-service-worker.js

@@ -0,0 +1,78 @@
+/**
+ * Twilio WP Plugin Service Worker
+ * Handles background notifications for incoming calls
+ */
+
+self.addEventListener('install', function(event) {
+    console.log('TWP Service Worker: Installing...');
+    self.skipWaiting();
+});
+
+self.addEventListener('activate', function(event) {
+    console.log('TWP Service Worker: Activated');
+    event.waitUntil(clients.claim());
+});
+
+// Handle notification clicks
+self.addEventListener('notificationclick', function(event) {
+    console.log('TWP Service Worker: Notification clicked');
+    event.notification.close();
+    
+    // Focus the window if it's already open, otherwise open a new one
+    event.waitUntil(
+        clients.matchAll({
+            type: 'window',
+            includeUncontrolled: true
+        }).then(function(clientList) {
+            // Check if there's already a window/tab open
+            for (let i = 0; i < clientList.length; i++) {
+                const client = clientList[i];
+                if (client.url.includes('/browser-phone') && 'focus' in client) {
+                    return client.focus();
+                }
+            }
+            // If not, open a new window
+            if (clients.openWindow) {
+                return clients.openWindow('/browser-phone');
+            }
+        })
+    );
+});
+
+// Handle push events (for future use with push notifications)
+self.addEventListener('push', function(event) {
+    console.log('TWP Service Worker: Push event received');
+    
+    let data = {};
+    if (event.data) {
+        try {
+            data = event.data.json();
+        } catch (e) {
+            data = {
+                title: 'New Call Alert',
+                body: event.data.text()
+            };
+        }
+    }
+    
+    const options = {
+        body: data.body || 'You have a new call waiting',
+        icon: data.icon || '/wp-content/plugins/twilio-wp-plugin/assets/images/phone-icon.png',
+        badge: '/wp-content/plugins/twilio-wp-plugin/assets/images/phone-badge.png',
+        vibrate: [300, 200, 300],
+        tag: data.tag || 'twp-notification',
+        requireInteraction: true,
+        data: data.data || {}
+    };
+    
+    event.waitUntil(
+        self.registration.showNotification(data.title || 'Incoming Call', options)
+    );
+});
+
+// Handle messages from the main script
+self.addEventListener('message', function(event) {
+    if (event.data && event.data.type === 'SHOW_NOTIFICATION') {
+        self.registration.showNotification(event.data.title, event.data.options);
+    }
+});