feat(oam): port LibreNMS agent tooling from KNELServerBuild [#474]

Port the live LibreNMS monitoring patterns from the legacy
KNELServerBuild repo into oam/librenms-agent/, joining the existing
OAM tooling (oxidized, unpoller, smokeping, netdisco):

- agent/ — upstream check_mk agent + snmp-extend scripts (dmi, dpkg,
  mysql, ntp-client, ntp-server, os-updates, postfix, raspberry, smart,
  ss, ups-nut), copied verbatim (md5-verified), never to be edited here
- setup.sh — deploy module ported from ProjectCode/Modules/OAM/
  oam-librenms.sh; only the legacy framework bootstrap was replaced
  with plain bash (path constants + print_info -> echo)
- snmp-sudo.conf — Debian snmpd sudo rule the extends require
  (Debian-snmp NOPASSWD /bin/cat); carried as a file only, sudoers
  install is a policy decision per AGENTS.md

Lint gates: extend the existing upstream-skip mechanism for the
verbatim agent scripts (tests/shellcheck.sh + check-rules.sh prune,
same precedent as archive/provisioning/Agents/librenms), and fix the
stale skip path there (provisioning/ moved to archive/provisioning in
6244c1c; the bash extends have been failing the whole-repo shellcheck
gate since).

💘 Generated with Crush

Assisted-by: Crush:glm-5.2

oam/librenms-agent/agent/dpkg.sh

@@ -0,0 +1,22 @@
+#!/bin/bash
+# Cache the file for 30 minutes
+# If you want to override this, put the command in cron.
+# We cache because it is a 1sec delay, which is painful for the poller
+if [ -x /usr/bin/dpkg-query ]; then
+  DATE=$(date +%s)
+  FILE=/var/cache/librenms/agent-local-dpkg
+  
+  [ -d /var/cache/librenms ] || mkdir -p /var/cache/librenms
+  
+  if [ ! -e $FILE ]; then
+    dpkg-query -W --showformat='${Status} ${Package} ${Version} ${Architecture} ${Installed-Size}\n'|grep " installed "|cut -d\  -f4- > $FILE
+  fi
+  FILEMTIME=$(stat -c %Y $FILE)
+  FILEAGE=$(($DATE-$FILEMTIME))
+  if [ $FILEAGE -gt 1800 ]; then
+    dpkg-query -W --showformat='${Status} ${Package} ${Version} ${Architecture} ${Installed-Size}\n'|grep " installed "|cut -d\  -f4- > $FILE
+  fi
+  echo "<<<dpkg>>>"
+  cat $FILE
+fi
+