fix usage with kdf setup for pin

by querying the card for the KDF DO (key derivation function data
object) the first time the PIN is used, applying the KDF (if any) to the
PIN, and saving & using the KDF-mangled PIN until cleared (or expired)

fix test_card to use a realistic test value

as an X25519 public key with all bits set is technically invalid
and may produce an error with some cards

Reported-by: rrottmann
Fixes: https://todo.sr.ht/~arx10/openpgpcard-wireguard-go/2

fix send_simple_command to handle get response

which is needed to derive shared secret with Gnuk firmware on a
STM32F103 (commercially available as Nitrokey Start or FST-01)

Co-authored-by: rrottmann
Fixes: https://todo.sr.ht/~arx10/openpgpcard-x25519-agent/1

sourcehut build script

links to other projects and usage in readme

basic install script

systemd unit files

change msg format/parse logging to info

ssh-agent client

allow systemd socket activation

move flake8 to pre-commit push hook

ssh-agent server

parse and format ssh-agent messages

calculate shared secret with card

show card info

py project scaffold

initial commit