feat(doorman): badge listener + decoder TDD + deploy scaffolding [#355]

Modern successor of the 2018 Perl doorman (snapshot in legacy/):
bash+coreutils HID decoder, HA webhook dispatch, systemd unit.
Offline decoder suite green (9 tests); shellcheck zero-warning.

Umbrella #345. Work item: https://projects.knownelement.com/issues/355

WORKING.md

@@ -0,0 +1,7 @@
+# WORKING — session scratchpad (cleared at session close)
+
+- [x] TDD: decoder suite red -> green (9 tests, tests/run-tests.sh)
+- [x] bin/doorman.sh listener (bash + coreutils only)
+- [x] systemd unit + /etc/default/doorman env refs
+- [x] shellcheck clean (tests/shellcheck.sh, docker)
+- [x] enforcement scripts adopted from TSYSGroupAIOS/PFVCluster