Make TURN/STUN port configurable via TURN_PORT env var

UniFi controller uses UDP 3478 for STUN, preventing coturn from
binding. Add TURN_PORT variable (default 3478) so users can set
TURN_PORT=3479 in .env to avoid the conflict.

https://claude.ai/code/session_01Vm6NLaQuzM4VosAotqS1q8

docker/entrypoint.sh

@@ -94,7 +94,7 @@ fi
 mkdir -p "$CONFIG_DIR"
 
 # Determine TURN/STUN server address
-turn_server="${TURN_SERVER:-${DOMAIN_NAME:-$local_ip}:3478}"
+turn_server="${TURN_SERVER:-${DOMAIN_NAME:-$local_ip}:${TURN_PORT:-3478}}"
 
 cat > "$CONFIG_FILE" << EOF
 # Easy Asterisk Configuration (Docker) - $(date)