feat(storage): CSI snapshots + smart-clone + migratable RWX for KubeVirt live-migration

Adds the VM/CDI storage tier approved by the PM (RWX for live-migration):

- platform/external-snapshotter (NEW, controllers pass): the cluster-singleton
  snapshot.storage.k8s.io control plane (CRDs + snapshot-controller in
  kube-system), pinned v8.2.0 (Kubernetes deps aligned to 1.31 since v8.1.0;
  this cluster is k3s v1.31.5). These CRDs were absent — only snapshots.longhorn.io
  and kubevirt.io snapshot CRDs existed.
- platform/longhorn/volumesnapshotclass.yaml (NEW, platform-config): the
  driver.longhorn.io VolumeSnapshotClass (type: snap, in-cluster).
- platform/kubevirt/cdi-storageprofiles.yaml (NEW, platform-config): StorageProfile
  longhorn -> cloneStrategy: snapshot; StorageProfile longhorn-vm -> snapshot clone
  + claimPropertySets RWX/Block. Non-degraded default virt class clears
  CDIDefaultStorageClassDegraded.
- platform/longhorn/storageclasses.yaml: NEW longhorn-vm StorageClass —
  migratable: "true" (Longhorn's KubeVirt-live-migration knob; RWX/Block-only on
  1.7.3), is-default-virt-class (NOT the k8s default; longhorn stays RWO default).
- platform/kubevirt/kubevirt-cr.yaml: comment only — LiveMigration is GA on v1.9
  (no feature gate); no cluster-wide evictionStrategy (would wedge RWO-disk drains);
  live-migration stays per-VM opt-in on a longhorn-vm disk.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

platform-config/kustomization.yaml

@@ -29,6 +29,10 @@ resources:
   # cilium: L2 LB IP pool + announcement policy (cilium.io CRDs already registered by Cilium)
   - cilium/l2-ip-pool.yaml
   - cilium/l2-announcement-policy.yaml
+  # longhorn/external-snapshotter: the driver.longhorn.io VolumeSnapshotClass (needs the
+  # snapshot.storage.k8s.io CRDs from platform/external-snapshotter). Enables CSI snapshots +
+  # CDI snapshot smart-clone.
+  - ../platform/longhorn/volumesnapshotclass.yaml
   # monitoring: PrometheusRule alert rules (need monitoring.coreos.com CRDs from kube-prometheus-stack)
   - ../platform/monitoring/alerts.yaml
   # kubevirt/cdi (Phase 5): the KubeVirt + CDI CRs consume the kubevirt.io / cdi.kubevirt.io CRDs the
@@ -37,6 +41,9 @@ resources:
   # ConfigMap kept beside them for locality.
   - ../platform/kubevirt/kubevirt-cr.yaml
   - ../platform/kubevirt/cdi-cr.yaml
+  # CDI StorageProfiles: snapshot smart-clone for `longhorn`, and RWX/Block + snapshot clone for the
+  # `longhorn-vm` virt-default class (consume cdi.kubevirt.io; clears CDIDefaultStorageClassDegraded).
+  - ../platform/kubevirt/cdi-storageprofiles.yaml
   - ../platform/kubevirt/servicemonitor.yaml
   - ../platform/kubevirt/alerts.yaml
   - ../platform/kubevirt/dashboard.yaml