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/longhorn/README.md

@@ -63,7 +63,7 @@ media on the replicated tier, or app DBs on the bulk tier.**
 - **OQ-2 (human):** decide the `bulk`-tier backing (NAS/NFS host + share, vs dedicated large disk).
   Until answered, the `bulk` class is a non-functional placeholder (`server`/`share` = REPLACE-ME).
   Blocks `bulk` finalize; does **not** block the core platform (docs/04).
-- **Version pin (WS-STORAGE):** `>=1.7.0 <1.8.0` is a range; pin exactly at bring-up, Renovate
+- **Version pin (WS-STORAGE):** `>=1.12.0 <1.13.0` is a range; pin exactly at bring-up, Renovate
   maintains.
 - **Phase 4 (WS-STORAGE):** off-cluster backup target via `defaultSettings.backupTarget` +
   SOPS-encrypted credential secret, wired alongside `platform/velero/` (R-STATE-03).