Node classes (draft)

Initial classes to minimize golden images while covering hardware/OS deltas:

rpi5-ubuntu-worker: Ubuntu 24.04, k3s agent, hardware=rpi5 (titan-04..11, 0a/0c minus control-plane bits)
rpi5-ubuntu-control: Ubuntu 24.04, k3s server (titan-0a/0b/0c specifics), control-plane taints, etcd snapshot hooks
rpi4-armbian-longhorn: Armbian 6.6.x, k3s agent, hardware=rpi4 with Longhorn disks (titan-13/15/17/19; astreae/asteria mounts)
rpi4-armbian-worker: Armbian 6.6.x, k3s agent, hardware=rpi4 without Longhorn disks; titan-16 uses the USB scratch recovery card standard
amd64-agent: Debian 13 k3s agent with GPU/node labels (titan-22/24, avoid by preference)
external-hosts: non-cluster (tethys, titan-db, titan-jh, oceanus/titan-23, future titan-20/21) – per-host config over base image template

Per-node overlays capture hostname/IP, labels/taints, Longhorn UUID mounts, USB scratch bind targets, and drop-ins for logging/GC.