Fix browser phone Twilio SDK loading and CSS layout issues

- Update Twilio SDK URL from sdk.twilio.com to unpkg CDN (same as backend)
- Change SDK version from 2.11.1 to 2.11.0 for consistency
- Fix dial number input overflow by adding box-sizing: border-box
- Ensure all elements use border-box sizing model

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

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

assets/css/browser-phone-frontend.css

@@ -7,6 +7,11 @@
     border-radius: 12px;
     box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
     font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
+    box-sizing: border-box;
+}
+
+.twp-browser-phone-container * {
+    box-sizing: border-box;
 }
 
 .twp-browser-phone-container.compact {