Make webtools host port configurable via WEBTOOLS_PORT

Port 80 on the host isn't always free (e.g. another service already bound
to it), so let .env override it like the game server ports already do.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docker-compose.yml

@@ -85,7 +85,7 @@ services:
     image: nginx:alpine
     restart: unless-stopped
     ports:
-      - "80:80"
+      - "${WEBTOOLS_PORT:-80}:80"
     volumes:
       - "./webtools:/usr/share/nginx/html:ro"
       - "./docker/conf/webtools-nginx.conf:/etc/nginx/conf.d/default.conf:ro"