getDisplayMedia (screen capture) requires a secure context, so LAN
staff access now goes through nginx on a real trusted cert
(local-summit.mydentalofficemanagement.com, issued via certbot's
Cloudflare DNS-01 plugin) instead of plain HTTP. A separate public
hostname/nginx block is reserved for Twilio webhooks only, routed
through Cloudflare Tunnel so nothing else is exposed to the internet.
Also fixes the backend CORS allowlist for the new hostname, and stops
the Socket.IO client from bypassing nginx to hit the backend directly
on :5000 (which broke under TLS/mixed content).
