Package: put the guard user in adm and systemd-journal

Only the unit's SupplementaryGroups gave them, so 'sudo -u guard guard
test' and 'guard check' could read neither /var/log's files nor the
journal. systemd-sysusers (run on every install and upgrade) adds them.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

deploy/sysusers.d/guard.conf

@@ -1,3 +1,7 @@
 # Guard's system user (systemd-sysusers): it reads logs and talks to
-# Housecarl, nothing more.
+# Housecarl, nothing more. adm reads /var/log's files, systemd-journal
+# the journal, for the daemon (its unit adds them too) and for
+# 'sudo -u guard guard test'.
 u guard - "Guard log watcher" /var/lib/guard /usr/sbin/nologin
+m guard adm
+m guard systemd-journal