proxmox: review fixes, real-host validation record, changelog

Phase 10. Two review passes (go-operator-reviewer, /code-review high)
over the branch, recorded in docs/reviews/2026-09-23-proxmox-provider-review/:
9 findings fixed, 3 accepted as documented limits, 7 rejected with a
reason.

- Delete removes the seed between the stop and the destroy, so a failed
  seed delete leaves the VM for the next Delete instead of leaking the
  ISO; a Permanent refusal on the every-node path fails the call.
- Create skips a probe VMID whose listed name is someone else's without
  waiting on its lock.
- The three answers Phase 0 never captured are fixtures now: a missing
  storage is a 400 (the Checker reports StorageNotFound), a hibernated
  VM is destroyable (Delete destroys ours), a paused VM stops.
- TestProxmox_lifecycle and TestProxmoxCheck_realHost passed on pv1-1
  (PVE 9.2.20); the docs record the run and drop "not yet run".

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

internal/provider/proxmox/testdata/task_status_stop_paused.json

@@ -0,0 +1,5 @@
+{
+  "status": 200,
+  "reason": "OK",
+  "body": "{\"data\":{\"upid\":\"UPID:pv1-1:0014F097:030A9433:6AB4DAE8:qmstop:199999:proxy-operator@pve!operator:\",\"status\":\"stopped\",\"exitstatus\":\"OK\",\"node\":\"pv1-1\",\"user\":\"proxy-operator@pve\",\"pstart\":51024947,\"pid\":1372311,\"id\":\"199999\",\"tokenid\":\"operator\",\"starttime\":1790237416,\"type\":\"qmstop\"}}"
+}