Copies /home/clawdie/.ssh/osa-mother-2026 (ed25519) from the build
host into the ISO at /home/clawdie/.ssh/osa-mother-2026 (0600).
Public key is in mother's authorized_keys. Lets the live USB node
SSH straight into the mother server without manual key exchange.
Skipped silently if the key file doesn't exist on the build host.