Uses ssh2 utils.parseKey() to check if the key decrypts and
parses correctly, logs the key type and public key fingerprint.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Logs key format, length, auth method selection, and ssh2 debug
output for auth/key events to diagnose why key auth is rejected.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>