Was only ever runnable once, buried inside base.sh's required-setup flow —
no way to re-run just this step for a box that already went through base
setup but needs another admin's key added later, or (the immediate case)
a home box for services/vpn-data-mount.sh that only needs this one step.
services/ssh-key-import.sh holds the real logic now (GitHub/Launchpad
import via ssh-import-id, optional password-auth lockdown); base.sh's
_base_setup_ssh chains into it the same way services/asterisk.sh chains
into security-dashboard/pstn-trunk, with a degraded (no import, just
ensures the SSH server itself is running) fallback for a pure standalone
`sudo bash base.sh` run with no sibling files sourced. Independently
runnable via `sudo ./setup.sh ssh-key-import` or `sudo bash
services/ssh-key-import.sh`, and shows up in the whiptail menu under
extras alongside ssh-config. Marked as never showing [installed] in
is_installed()/install_count(), same as ssh-config — it's a repeatable
management action, not a thing with an install state.
