docs: reconcile docs/comments with post-upgrade cluster state

Text-only cleanup after the upgrade campaign. Updates stale version
strings, prose, and comments to the verified current facts; no
Kubernetes behavior or version pins changed except the kubectl
toolchain bump (below).

Verified facts applied: k3s v1.36.4+k3s1, Debian 13 trixie,
Cilium 1.20.1 / Gateway API v1.6.1, Longhorn 1.12.1, node RAM 24 GiB,
dedicated virtio2 SSD etcd disk per node, Velero chart 12.x / v1.18,
Grafana 13.2.0.

- Version strings across infra/ and platform/ READMEs + comments
- kubectl toolchain 1.31.4 -> 1.36.4 (devcontainer/ci/conformance
  versions.env; 1.31 vs a 1.36 cluster exceeded the +-1 skew)
- Retired-single-apps-Kustomization refs -> apps-wave-0/1/2 + apps-vms
  with per-wave SOPS decryption (flux/clusters docs + bootstrap.sh)
- COMPLETED/historical banners on the three executed plan docs
- Resolved TODO(WS-SEC) markers -> Renovate-maintained ranges
- Appended dated DECISIONS-LOG entry (2026-08-30) superseding the
  2026-08-26 LIVE STATE line

Left as revalidation items (not blind-edited): external-snapshotter
v8.2.0 vs 1.36, Cilium ext_authz/forward-auth relevance under 1.20.1,
conformance ImageVolume feature-gate assertions under 1.36.

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

platform/external-snapshotter/README.md

@@ -26,6 +26,7 @@ Neither k3s nor the Longhorn chart ships this. It is a prerequisite for:
 ## Version
 
 Pinned to **v8.2.0** (Renovate-maintained). The v8.x line aligned to Kubernetes 1.31 at
-v8.1.0; this cluster is k3s v1.31.5. The snapshot-controller image is re-pinned to the same
-tag via the kustomization `images` transformer (the upstream setup manifest lags on the image
-tag).
+v8.1.0; this cluster is now k3s v1.36.4, so the pin should be **re-checked for 1.36** (a newer
+external-snapshotter line may be the version-matched choice) — do not treat v8.2.0 as verified
+against 1.36 yet. The snapshot-controller image is re-pinned to the same tag via the kustomization
+`images` transformer (the upstream setup manifest lags on the image tag).

platform/external-snapshotter/kustomization.yaml

@@ -18,9 +18,10 @@
 # CRDs (the Longhorn VolumeSnapshotClass, item 2) live in platform-config so the CRDs exist first.
 #
 # VERSION (Renovate-maintained): external-snapshotter v8.2.0.
-#   * The v8.x line updated its Kubernetes deps to 1.31 at v8.1.0 (this cluster is k3s v1.31.5),
-#     so v8.2.x is the conservative, version-matched choice — newer than the 1.31 alignment,
-#     older than the v8.4/v8.5 churn.
+#   * The v8.x line updated its Kubernetes deps to 1.31 at v8.1.0. This cluster is now k3s v1.36.4,
+#     so the v8.2.0 pin is NO LONGER verified against the running Kubernetes version — RE-CHECK it
+#     for 1.36 (a newer external-snapshotter line may be the version-matched choice). Pin left as-is
+#     pending that revalidation.
 #   * snapshot.storage.k8s.io CRDs are served at v1 (GA) — driver.longhorn.io speaks v1, so
 #     Longhorn CSI snapshots + CDI snapshot-clone work against these CRDs.
 #   * The upstream setup manifest pins the controller image to an older v8.0.x tag; the `images`