Add informative status messages and improve image customization flow: install base packages and Docker during virt-customize, enable Docker service, and configure /etc/docker/daemon.json (sets DOCKER_PREINSTALLED on success). Add finalization messages while setting hostname and SSH config. For images without cloud-init, add systemd drop-ins to enable root autologin on serial-getty@ttyS0 and getty@tty1. Also add a trailing newline to nginx-ui.json.
