thermal: van-thermal daemon (CPU+NVMe monitor, alert, log)

Single sysfs sample loop drives three jobs off one daemon (modeled on
van-failover):

- live state at /run/van-thermal/state.json; new Cockpit "Temperatures"
  card reads it in the existing 5s loop (no per-refresh `sensors` shell-out)
- journal alerts on ok<->warn<->crit crossings, with clear_margin hysteresis
- throttled, self-rotating CSV history at /var/log/van-thermal.csv

Sensors resolved by hwmon name+label (coretemp/Package id 0, nvme/Composite),
never by hwmonN index (not stable across boots). Defaults: CPU warn 80 /
crit 95, NVMe warn 65 / crit 70. deploy.sh installs + enables the service.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

power/van-thermal.service

@@ -0,0 +1,12 @@
+[Unit]
+Description=Temperature monitor (CPU + NVMe) for the campervan router
+After=local-fs.target
+
+[Service]
+Type=simple
+ExecStart=/usr/local/sbin/van-thermal
+Restart=always
+RestartSec=5
+
+[Install]
+WantedBy=multi-user.target