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]>

catalog/render.py

@@ -464,7 +464,7 @@ def r_gateway_ingress_policy(s: dict):
     north-south). This CiliumNetworkPolicy is the ADDITIVE, least-privilege allow that opens
     ONLY the north-south path (docs/09 "Ingress opens north-south only — it does not relax
     east-west default-deny"): ingress from Cilium's reserved `ingress` identity (the Gateway/
-    Ingress Envoy proxy, `reserved:ingress`, numeric identity 8 in Cilium 1.16.5) to ONLY the
+    Ingress Envoy proxy, `reserved:ingress`, numeric identity 8 in Cilium 1.20.1) to ONLY the
     exposed service port(s). Everything else stays denied; undeclared ports stay denied.
 
     Verified empirically against the cluster: with default-deny in place, Hubble shows the