TURN fixes

Mirror of upstream coop-cloud/lasuite-meet#6:
- fix: resolve TURN_DOMAIN default at .env layer (compose.yml does not
  recursively expand nested ${...} references)
- docs: document host UDP buffer sysctl tuning for LiveKit
- docs: mention Chrome required on mobile
- docs: fix ports table formatting

Upstream: https://git.coopcloud.tech/coop-cloud/lasuite-meet/pulls/6

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.sample

@@ -82,7 +82,9 @@ LIVEKIT_NODE_IP=
 #LIVEKIT_TURN_ENABLED=false
 ## TURN domain — must resolve to this server's IP.
 ## Defaults to LIVEKIT_DOMAIN, which works for TURN/UDP setups.
-#TURN_DOMAIN=turn.example.com
+## NOTE: must be set here, not as a compose-level `:-` default —
+## docker-compose does not recursively expand nested `${...}` references.
+TURN_DOMAIN=${LIVEKIT_DOMAIN}
 ## TURN/UDP port (default: 443). Recommended because UDP 443 is rarely
 ## blocked and doesn't conflict with Traefik's TCP 443.
 #TURN_UDP_PORT=443