feat(pdu): garage PDU SNMP relay on tsys-librenms (AP7830 v1-only) [#344]

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Assisted-by: Crush:glm-5.2

dcinfra/sensors/pdu/garage-pdu-relay.sh

@@ -0,0 +1,20 @@
+#!/bin/bash
+# garage-pdu-relay: expose APC AP7830 metered output current via snmpd extend.
+#
+# Relay pattern (founder ruling 2026-09-02): the garage PDU speaks SNMPv1
+# only, walks die on its old AOS, and its ACL admits the LibreNMS VM vantage.
+# This relay runs ON tsys-librenms; HA polls the relay via the fleet snmpd
+# extend (same rails as drac-extend). Output: "output_amps <x.y>".
+set -euo pipefail
+
+PDU_HOST="${PDU_HOST:-pfv-garage-pdu-1.knel.net}"
+COMMUNITY="${PDU_COMMUNITY:-kn3lmgmt}"
+OID=".1.3.6.1.4.1.318.1.1.12.2.3.1.1.2.1"
+
+raw=$(snmpget -v1 -c "$COMMUNITY" -On -Ov "$PDU_HOST" "$OID" 2>/dev/null \
+    | grep -oE '[0-9]+$') || true
+if [ -z "${raw:-}" ]; then
+    echo "output_amps unavailable"
+    exit 0
+fi
+awk -v t="$raw" 'BEGIN { printf "output_amps %.1f\n", t/10 }'