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

.env.example

@@ -0,0 +1,3 @@
+# Refs only — real values live in ~/.creds (0600), never in repos.
+# Example: this repo's CLIs read env files at runtime, e.g.
+#   docker run --rm --env-file ~/.creds/redmine.env ...