[prop4n]

Adds arbitrary cloud-init user-data, delivered 100% over the API (no SSH, no
snippets). Proxmox's native cloud-init options can't carry raw user-data, and
snippets need file access to the node; instead proxmops generates a NoCloud
CIDATA seed ISO from spec.userData, uploads it, and attaches it as a cdrom.
Any NoCloud consumer (cloud-init, guix-metadata) reads it at boot.

Manifest

spec:
  fromTemplate: guix-homelab-template
  userData: |
    #cloud-config
    ((system-file . "systems/web01.scm"))
  applyMode: reboot
  state: running

userData is mutually exclusive with cloudInit and iso (all three drive the
cidata disk / ide0).

How

• internal/proxmox/cidata.go: build the CIDATA ISO with go-diskfs; upload via a
  raw multipart POST (the go-proxmox SDK's Upload mis-formats the body); resolve an
  iso-content storage; delete old seeds.
• The ISO is named proxmops-cidata-<vmid>-<hash8>.iso, so the attached ide0
  encodes which user-data is live.
• Create paths (blank/image/clone) provision it; the Proxmox cloud-init drive
  (ide2) is skipped when userData is set (would be a second cidata disk).

Re-sync (scope B)

• The reconciler compares the desired user-data hash to the hash in the observed
  ide0. On a change it re-provisions (upload new, attach, delete old).
• A stopped VM reads the new seed on next boot, so it is re-provisioned right away.
• A running VM needs a reboot to re-read it: done when applyMode: reboot, else
  reported as "reboot required".
• The seed ISO is deleted when the VM is deleted, so none accumulate.

Verification

• Unit: ISO build + read-back (label CIDATA, payload), deterministic hash,
  parse helpers, manifest exclusivity, and the reconciler drift branches
  (running+reboot, running+informational, stopped+reprovision, no-drift).
• End-to-end on the live cluster, driven by the daemon: create attaches the
  right cidata ISO (hash matches content, no ide2); changing userData
  re-provisions the new ISO, deletes the old one, and reboots only a running VM.
• The upload API and go-diskfs generation were proven with a spike before design.

golangci-lint (v2), gofmt, Go + vitest suites green. Promotes go-diskfs to a
direct dependency.