Implement Discord and Slack notifications for call events

Settings & Configuration:
- Added Discord webhook URL, Slack webhook URL settings in admin
- Added notification type toggles (incoming calls, queue timeouts, missed calls)
- Added queue timeout threshold setting (30-1800 seconds)
- Registered all new settings with WordPress options system

Notification System:
- Created TWP_Notifications class for Discord/Slack webhook handling
- Rich message formatting with embeds/attachments for both platforms
- Color-coded notifications (blue=incoming, yellow=timeout, red=missed)
- Comprehensive error handling and logging

Integration Points:
- Incoming calls: Notifications sent when calls enter queues
- Queue timeouts: Automated monitoring via cron job (every minute)
- Missed calls: Notifications for browser phone and general missed calls
- Added notified_timeout column to prevent duplicate timeout notifications

Features:
- Professional Discord embeds with fields and timestamps
- Slack attachments with proper formatting and colors
- Automatic cron job setup for queue timeout monitoring
- Fallback to SMS notifications while Discord/Slack also work
- Configurable notification types and timeout thresholds

This provides real-time call notifications to Discord channels and Slack channels,
helping teams stay informed about incoming calls and queue issues even when
SMS notifications aren't working due to validation delays.

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

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

includes/class-twp-activator.php

@@ -366,6 +366,12 @@ class TWP_Activator {
         if (empty($status_index_exists)) {
             $wpdb->query("ALTER TABLE $table_queued_calls ADD INDEX status (status)");
         }
+        
+        // Add notified_timeout column for Discord/Slack notifications
+        $notified_timeout_exists = $wpdb->get_results("SHOW COLUMNS FROM $table_queued_calls LIKE 'notified_timeout'");
+        if (empty($notified_timeout_exists)) {
+            $wpdb->query("ALTER TABLE $table_queued_calls ADD COLUMN notified_timeout datetime AFTER agent_call_sid");
+        }
     }
     
     /**