A Frame that only authorizes the user's own key refused OpenSSH, which
offered FramePort's keys alone (IdentitiesOnly), so every upload fell back
to Paramiko. The connection now records which login worked (Frame.auth):
after a login with this PC's own keys/agent OpenSSH also offers private
copies of ~/.ssh/id_* (OpenSSH skips its defaults once -i is given) and the
agent; a refused strict login is retried that way once. FramePort doesn't
add its key to the Frame for this.
New: Settings > Installing > SSH keys (library ssh.extra_keys, CLI
frameport frame ssh-keys): extra private key files for the connection and
OpenSSH, checked with Paramiko (passphrase keys: use the agent). OpenSSH
runs with -v and a refused login's error lists the keys offered and its
warnings. whoami's SID is read from bytes (non-ASCII user names).
Checked with Windows ssh.exe/sftp.exe against the Frame.
