Wraps ssh-key's PublicKey::fingerprint(HashAlg::Sha256). Output format
matches ssh-keygen -lf and git verify-commit --raw stderr
(SHA256:<43-char base64>). Used by the upcoming relicario-server
verify-commit rewrite (audit S1).
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
OpenSSH-format keypair generation, signing, and verification.
Foundation for device authentication.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>