Add queue timeout voicemail and Amazon SNS SMS provider support

This update adds two major features:

1. Queue Timeout Voicemail
   - Callers can now leave voicemail when queue timeout is reached
   - Configurable per-queue voicemail prompts with TTS support
   - Automatic transcription and urgent keyword detection
   - Admin setting to choose between voicemail or callback on timeout

2. Amazon SNS SMS Provider
   - Alternative SMS provider to Twilio for sending text messages
   - Useful when Twilio SMS approval is difficult to obtain
   - Provider abstraction layer allows switching between Twilio/SNS
   - Full AWS SNS configuration in admin settings
   - Supports custom sender IDs in compatible countries
   - Lower cost per SMS compared to Twilio

New Files:
- includes/class-twp-voicemail-handler.php - Voicemail recording handler
- includes/interface-twp-sms-provider.php - SMS provider interface
- includes/class-twp-sms-provider-twilio.php - Twilio SMS implementation
- includes/class-twp-sms-provider-sns.php - Amazon SNS implementation
- includes/class-twp-sms-manager.php - SMS provider abstraction manager
- QUEUE_VOICEMAIL_SMS_FEATURES.md - Complete feature documentation

Modified Files:
- includes/class-twp-call-queue.php - Added voicemail option to timeout handler
- includes/class-twp-twilio-api.php - Updated send_sms() to use provider abstraction
- admin/class-twp-admin.php - Added SMS provider and timeout action settings
- composer.json - Added AWS SDK dependency

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

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

includes/class-twp-twilio-api.php

@@ -275,49 +275,12 @@ class TWP_Twilio_API {
     }
     
     /**
-     * Send SMS
+     * Send SMS (uses configured SMS provider - Twilio or Amazon SNS)
      */
     public function send_sms($to_number, $message, $from_number = null) {
-        try {
-            // Determine the from number
-            $from = $from_number ?: $this->phone_number;
-            
-            // Validate we have a from number
-            if (empty($from)) {
-                error_log('TWP SMS Error: No from number available. Please configure SMS notification number in settings.');
-                return [
-                    'success' => false,
-                    'error' => 'No SMS from number configured. Please set SMS notification number in plugin settings.'
-                ];
-            }
-            
-            $sms = $this->client->messages->create(
-                $to_number,
-                [
-                    'from' => $from,
-                    'body' => $message
-                ]
-            );
-            
-            return [
-                'success' => true,
-                'data' => [
-                    'sid' => $sms->sid,
-                    'status' => $sms->status,
-                    'from' => $sms->from,
-                    'to' => $sms->to,
-                    'body' => $sms->body,
-                    'price' => $sms->price,
-                    'priceUnit' => $sms->priceUnit
-                ]
-            ];
-        } catch (\Twilio\Exceptions\TwilioException $e) {
-            return [
-                'success' => false,
-                'error' => $e->getMessage(),
-                'code' => $e->getCode()
-            ];
-        }
+        // Use SMS Manager to handle provider abstraction
+        require_once dirname(__FILE__) . '/class-twp-sms-manager.php';
+        return TWP_SMS_Manager::send_sms($to_number, $message, $from_number);
     }
     
     /**