docs: correct CI/platform documentation that was stale, wrong, or load-bearing

The 2026-09-29 session found the merge gate did not exist -- no branch protection, no
runner -- while the tree asserted both. This corrects the documents that carried, and in
several cases CAUSED, that belief.

CLAUDE.md gains section 2b: never infer platform state from this repository. It carries
the specific API and kubectl checks for protection, runners, CI status, workloads and
Flux revisions, and the rule that a green tick is not proof anything ran (a skipped Gitea
job reports success). This is the rule whose absence produced every other finding.

.gitea/workflows/README.md and merge-gate.yaml both said "there is no remote git host,
this file is dormant". Gitea had been live for weeks. Both were written as plans and never
revisited once the plan completed. The Transition section is now marked COMPLETE and says
what is genuinely still outstanding (CLUSTER_AVAILABLE unset, so L2/L3 never runs in CI).

DECISIONS-LOG 2026-08-31 is annotated IN PLACE. Anyone reading chronologically previously
hit "required status check; runner incluster-dind online" with nothing marking it false
until a month later. The correction now sits on the bullet itself.

ci/README.md, clusters/README.md and both conformance READMEs carry a status banner: they
speak as though no cluster exists, which makes a live L2/L3 coverage gap read as an
expected phase. That framing is why the gap went unexamined.

apps/wave-1/gitea-actions-runner-secret.sops.yaml: fixed a wrong path, replaced advice to
`sops -d` into a terminal (which CLAUDE.md forbids) with the rotation script, and recorded
that a fresh token alone does not re-register a runner holding a stale /data/.runner.

apps/wave-0/plex-claim-secret.sops.yaml: the header claimed the file ships the placeholder.
It has not since the claim -- it holds the spent token, which is inert and deliberately
left in place.

catalog/plex.yaml and the plex secret both asserted a "~4-minute TTL" as fact. It was
uncited, upstream documents no expiry, and it was the basis for a since-disproven claim
that the pipeline was too slow to fit inside it. Measured: ~2m45s.

Both .sops.yaml files were verified to still decrypt after the comment edits
(`sops -d > /dev/null`), and render==golden confirms the catalog comment does not
propagate into the rendered manifest.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

clusters/README.md

@@ -1,5 +1,19 @@
 # clusters/
 
+> **STATUS NOTE (2026-09-29) — read before trusting the "Phase 0" framing below.**
+> This document speaks as though no cluster exists and the platform is scaffolding. **A
+> three-node k3s cluster has existed for weeks** and Flux has been reconciling against it.
+> Gitea is live, the Actions runner `incluster-dind` is online, and `main` is a protected
+> branch. Where the text says "Phase 0", "stub", or "no cluster exists", read it as
+> describing a **live gap** rather than an expected stage — most importantly, L2/L3
+> conformance still does not run in CI (`vars.CLUSTER_AVAILABLE` is unset), which is a real
+> coverage hole, not a phase.
+>
+> This mismatch is not cosmetic. A month of "the gate enforces this" claims rested on
+> documentation rather than measurement, and `main` was unprotected with zero runners
+> registered the whole time. **Query the live API before asserting platform state.**
+
+
 Flux entrypoints and the environment-overlay model (**R-ENV-02**, **R-GITOPS-01/02/03**).
 
 Governing spec: [`docs/05-gitops-and-delivery.md`](../../home-network-k3s/docs/05-gitops-and-delivery.md),