Card reading (rdm6300 + pyserial) printing card inserted/removed with the
full card data, plus a --serve mode that publishes taps over HTTP so a web
page can authenticate a tap.
The bridge reports card ids only - mapping a card to a user stays on the
server. The tap is latched for --tap-ttl seconds, including after the card is
lifted, and is single use, so a page reload cannot replay one tap into two
logins.
Port selection identifies the reader by serial number or by-id path instead of
/dev/ttyUSBn, and refuses to guess when a selector matches several adapters.
deploy/ has the systemd unit, a udev rule for a stable /dev/rdm-reader, and
install.sh. Covered by unit tests plus PTY end-to-end tests.
