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/css/browser-phone-frontend.css

@@ -261,6 +261,23 @@
     transform: translateY(-1px);
 }
 
+.twp-btn-info {
+    background: #17a2b8;
+    color: white;
+    border: none;
+    padding: 10px 20px;
+    border-radius: 6px;
+    cursor: pointer;
+    font-size: 14px;
+    font-weight: 500;
+    transition: all 0.2s ease;
+}
+
+.twp-btn-info:hover {
+    background: #138496;
+    transform: translateY(-1px);
+}
+
 /* Call Info */
 .twp-call-info {
     background: #fff;