wolf-pair runs network_mode: host, so a taken 8090 fails at container
start with "address already in use" and no ports: line in
docker-compose.yml to explain why — wordpress, ntfy, and beszel all
default to 8090 too and correctly scan for a free port; wolf-pair
hardcoded it in three places (installer var, UFW rule, server.py's
bind) with no scan at all.
Now finds a free port via find_free_port, persists it in a new .env
(read back on rerun so a live install never silently moves), and
threads it into the container via WOLFPAIR_PORT so server.py binds
the scanned port instead of a literal 8090.
Claude