chore: initial import from KNEL/PFVCluster@041d311 [#769]

Split per O&M lane work order. Full history: KNEL/PFVCluster.
shellcheck debt fixed in librenms-agent (quoting, arithmetic, backticks);
fixes upstream ntp-server.sh bug: input_wakeups reported PACKETSENDFAILURES
instead of INPUTWAKEUPS. mysql.sh (PHP-in-.sh) exempt per house rule.

https://projects.knownelement.com/issues/769#note-4152

AGENTS.md

@@ -0,0 +1,8 @@
+# AGENTS.md — monitoring
+
+Point of truth for fleet-wide agent policy: the workspace AGENTS.md in KNEL/PFVCluster (loaded globally). This file holds repo-specific notes only.
+
+- Ticket gate: `echo '#NNN' > .crush/active-ticket` before any modification; reference [\#343] + [#769].
+- Remote access: SSH chokepoints only — tests/remote.sh (PFVCluster)monitoring; DNS names only, never IP literals.
+- Docs: Discourse topic https://community.turnsys.com/t/323 — keep README pointer current.
+- shellcheck zero-warning (incl. info) via `bash tests/shellcheck.sh`.