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

Dockerfile

@@ -30,6 +30,27 @@ COPY services/ services/
 
 CMD ["python", "-u", "poller.py"]
 
+# ---- Target: host-poller (chassis IPMI/iDRAC + CPU + on-metal drives) ----
+# Privileged at runtime (needs /dev/ipmi0 + raw disks). Carries ipmitool +
+# smartmontools; no SAS-shelf tooling.
+FROM python:3.13-slim AS host-poller
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    ipmitool \
+    smartmontools \
+    util-linux \
+    && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /app
+
+COPY requirements-poller.txt .
+RUN pip install --no-cache-dir -r requirements-poller.txt
+
+COPY host_poller.py .
+COPY services/ services/
+
+CMD ["python", "-u", "host_poller.py"]
+
 # ---- Target: web (read-only consumer) ----
 # Unprivileged at runtime; no hardware tools. Serves REST/UI + MQTT, reads Redis.
 FROM python:3.13-slim AS web