Fix voicemail access and ElevenLabs voice loading issues

- Changed create_voicemail_twiml() from private to public method to fix fatal error when accessing voicemail from IVR
- Added auto-loading of ElevenLabs voices when switching to TTS option for new workflow steps
- Voices now load automatically when user selects "Use Text-to-Speech" radio button

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

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

assets/js/admin.js

@@ -1701,6 +1701,15 @@ jQuery(document).ready(function($) {
         // Show the appropriate options based on selection
         if (audioType === 'tts') {
             $ttsOptions.show();
+            
+            // Auto-load voices if they haven't been loaded yet
+            var $voiceSelect = $ttsOptions.find('.voice-select');
+            if ($voiceSelect.length && $voiceSelect.find('option').length <= 1) {
+                // Check if API key exists before auto-loading
+                if (twp_ajax.has_elevenlabs_key) {
+                    loadWorkflowVoices($voiceSelect[0]);
+                }
+            }
         } else if (audioType === 'audio') {
             $audioOptions.show();
         }