live-config's openssh-server component rewrites sshd_config to
"PasswordAuthentication no" on every live boot, so the live session only
accepted SSH keys. An sshd_config.d drop-in sets it back to yes; sshd uses
the first value it reads and sshd_config includes the drop-ins first, so the
drop-in wins. The login is user / live (live-config's default), now noted
in INSTALL.md. check-iso.sh fails the build if the drop-in is missing.
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
