Adds cmd/installer with three packages:
- ui: huh-based TUI collecting disk, network, node, and cluster config
- install: sequential install steps (partition, debootstrap, chroot, bootloader)
- firstboot: oneshot systemd service that runs setup-ovn and spx admin init/join on first real boot
Supports both single-node init and multi-node join flows.
tomnewton-mulga