Fix browser phone connection and audio issues on Android tablets

Resolves issues where browser phone PWA failed to connect and calls would
immediately hang up when answered on Android tablets. Adds proper mobile
audio handling, device connection monitoring, and PWA notifications for
incoming calls.

Key changes:
- Add AudioContext initialization with mobile unlock for autoplay support
- Add Android-specific WebRTC constraints (echo cancellation, ICE restart)
- Add device connection state monitoring and auto-reconnection
- Add incoming call ringtone with vibration fallback
- Add PWA service worker notifications for background calls
- Add Page Visibility API for background call detection
- Improve call answer handler with connection state validation
- Add touch event support for mobile dialpad

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

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

assets/js/twp-service-worker.js

@@ -72,7 +72,23 @@ self.addEventListener('push', function(event) {
 
 // Handle messages from the main script
 self.addEventListener('message', function(event) {
+    console.log('TWP Service Worker: Message received', event.data);
+
     if (event.data && event.data.type === 'SHOW_NOTIFICATION') {
-        self.registration.showNotification(event.data.title, event.data.options);
+        const options = {
+            body: event.data.body || 'You have a new call waiting',
+            icon: event.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, 200, 300],
+            tag: event.data.tag || 'incoming-call',
+            requireInteraction: event.data.requireInteraction !== undefined ? event.data.requireInteraction : true,
+            data: event.data.data || {}
+        };
+
+        console.log('TWP Service Worker: Showing notification', event.data.title, options);
+
+        event.waitUntil(
+            self.registration.showNotification(event.data.title || 'Incoming Call', options)
+        );
     }
 });