Enable Docker and expose the daemon over TCP 2375 by extending the systemd
docker.socket ListenStream (avoids the daemon.json hosts vs unit -H fd://
conflict). The port is not added to allowedTCPPorts; instead an nftables
rule accepts it only from the trusted LAN subnet. Plain 2375 is
root-equivalent, so the source restriction is the only safeguard -- mTLS on
2376 is the documented upgrade path.
Emma Thorpe