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-core.php

@@ -167,6 +167,10 @@ class TWP_Core {
         
         // Agent queue management AJAX
         $this->loader->add_action('wp_ajax_twp_accept_call', $plugin_admin, 'ajax_accept_call');
+        
+        // Discord/Slack notification system
+        $this->loader->add_action('init', $this, 'setup_notification_cron');
+        $this->loader->add_action('twp_check_queue_timeouts', $this, 'check_queue_timeouts');
         $this->loader->add_action('wp_ajax_twp_accept_next_queue_call', $plugin_admin, 'ajax_accept_next_queue_call');
         $this->loader->add_action('wp_ajax_twp_get_waiting_calls', $plugin_admin, 'ajax_get_waiting_calls');
         $this->loader->add_action('wp_ajax_twp_set_agent_status', $plugin_admin, 'ajax_set_agent_status');
@@ -385,4 +389,21 @@ class TWP_Core {
             error_log("TWP Cleanup: Updated {$updated_waiting} old waiting calls to 'timeout' status");
         }
     }
+    
+    /**
+     * Setup notification cron job
+     */
+    public function setup_notification_cron() {
+        if (!wp_next_scheduled('twp_check_queue_timeouts')) {
+            wp_schedule_event(time(), 'twp_every_minute', 'twp_check_queue_timeouts');
+        }
+    }
+    
+    /**
+     * Check for queue timeouts and send notifications
+     */
+    public function check_queue_timeouts() {
+        require_once dirname(__FILE__) . '/class-twp-notifications.php';
+        TWP_Notifications::check_queue_timeouts();
+    }
 }