Speed up browser phone initialization

- Add preload hint for Twilio SDK to start loading earlier
- Add DNS prefetch and preconnect for Twilio servers
- Check SDK immediately instead of waiting 500ms
- Reduce polling interval from 100ms to 50ms

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

admin/class-twp-admin.php

@@ -7445,6 +7445,11 @@ class TWP_Admin {
             }
             </style>
             
+            <!-- Preload and preconnect for faster loading -->
+            <link rel="preload" href="https://unpkg.com/@twilio/voice-sdk@2.11.0/dist/twilio.min.js" as="script">
+            <link rel="dns-prefetch" href="//unpkg.com">
+            <link rel="dns-prefetch" href="//chunderw-vpc-gll.twilio.com">
+            <link rel="preconnect" href="https://chunderw-vpc-gll.twilio.com" crossorigin>
             <!-- Twilio Voice SDK v2 from unpkg CDN -->
             <script src="https://unpkg.com/@twilio/voice-sdk@2.11.0/dist/twilio.min.js"></script>
             <script>
@@ -8235,7 +8240,7 @@ class TWP_Admin {
                 // Check if SDK loaded and initialize
                 // Poll for Twilio SDK availability (window.load may not fire on mobile)
                 var sdkCheckAttempts = 0;
-                var maxSdkCheckAttempts = 50; // 5 seconds max
+                var maxSdkCheckAttempts = 100; // 5 seconds max (100 * 50ms)
 
                 function checkAndInitialize() {
                     sdkCheckAttempts++;
@@ -8244,16 +8249,23 @@ class TWP_Admin {
                         console.log('Twilio SDK loaded successfully');
                         initializeBrowserPhone();
                     } else if (sdkCheckAttempts < maxSdkCheckAttempts) {
-                        // Keep checking every 100ms
-                        setTimeout(checkAndInitialize, 100);
+                        // Keep checking every 50ms for faster response
+                        setTimeout(checkAndInitialize, 50);
                     } else {
                         showError('Twilio Voice SDK failed to load. Please check your internet connection and try refreshing the page.');
                         console.error('Twilio SDK not found after ' + sdkCheckAttempts + ' attempts.');
                     }
                 }
 
-                // Start checking after a brief delay
-                setTimeout(checkAndInitialize, 500);
+                // Check immediately - SDK script is synchronous so should be loaded
+                // If not ready yet (mobile), polling will catch it
+                if (typeof Twilio !== 'undefined' && Twilio.Device) {
+                    console.log('Twilio SDK already loaded');
+                    initializeBrowserPhone();
+                } else {
+                    // Start polling immediately
+                    checkAndInitialize();
+                }
 
                 // Also keep the window.load as backup for desktop
                 $(window).on('load', function() {