Enhance browser phone with real-time updates and audible alerts

- Fix token expiration: Extend refresh buffer to 10 minutes for reliability
- Add real-time queue updates: Reduce polling to 5 seconds for instant feedback
- Implement audible alert system: 30-second repeating notifications with user toggle
- Optimize Discord/Slack notifications: Non-blocking requests for immediate delivery
- Add persistent alert preferences: Toggle button with localStorage integration
- Clean up debug file: Remove unused debug-phone-numbers.php

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

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

includes/class-twp-shortcodes.php

@@ -193,6 +193,9 @@ class TWP_Shortcodes {
                         <button id="twp-refresh-queues" class="twp-btn twp-btn-secondary">
                             Refresh
                         </button>
+                        <button id="twp-alert-toggle" class="twp-btn twp-btn-secondary alert-off">
+                            🔕 Alerts OFF
+                        </button>
                     </div>
                 </div>
             </div>