Add host-poller: chassis IPMI/iDRAC + CPU + on-metal drive temps

New third producer container (host-poller) owning the server chassis
subsystem, separate from the SAS-shelf poller:
- services/host_sensors.py: in-band IPMI (ipmitool sdr) for Inlet/Exhaust/etc.
  + CPU package temps from coretemp hwmon
- host_poller.py: own single-instance lock + heartbeat (host_poll keys),
  restart-storm guard, paced; writes jbod:host_sensors + jbod:host_drives
- move host/on-metal drive collection off the SAS poller to host-poller
  (reads jbod:zfs_map for annotation)
- store: generalized lock/meta with a key param; host_sensors + host-poll keys
- mqtt_publisher: publish env/CPU/host-drive temps as entities on the hub
  device (JBOD Monitor)
- Dockerfile host-poller target (ipmitool+smartmontools); compose.infra adds
  host-poller; build.sh gains host-poller/all

build.sh

@@ -16,10 +16,11 @@ cd "$(dirname "$0")"
 # First arg is the target if it's a known one; otherwise it's treated as the
 # commit message (backward-compatible with `./build.sh "message"`).
 case "${1:-}" in
-    poller) TARGETS="poller"; MSG="${2:-Build and push images}" ;;
-    web)    TARGETS="web";    MSG="${2:-Build and push images}" ;;
-    all|"") TARGETS="poller web"; MSG="${2:-Build and push images}" ;;
-    *)      TARGETS="poller web"; MSG="${1}" ;;
+    poller)      TARGETS="poller";      MSG="${2:-Build and push images}" ;;
+    host-poller) TARGETS="host-poller"; MSG="${2:-Build and push images}" ;;
+    web)         TARGETS="web";         MSG="${2:-Build and push images}" ;;
+    all|"")      TARGETS="poller host-poller web"; MSG="${2:-Build and push images}" ;;
+    *)           TARGETS="poller host-poller web"; MSG="${1}" ;;
 esac
 TARGET="${TARGETS// /+}"