docs(nav): publish every ADR and runbook, gated by a nav check (closes #169) (#172)

## What & why

`docs/` is the source of truth (CLAUDE.md §12), but only pages listed in `mkdocs.yml`'s nav
are published — and mkdocs' own `validation.nav.omitted_files: warn` keeps the build green
while dropping the rest. So the site had quietly stopped at **ADR-0010** and
**`runbooks/ci.md`**: 31 pages, including every ADR from 0011 to 0034, six of the seven
runbooks, and `synthetic-data.md`, existed in the repo and nowhere else.

- `infra/check-docs-nav.py` fails when a page under `docs/` is not in the nav. It runs in
  `make lint`, so the existing CI job gates it — python3 only, no new tooling, and no
  mkdocs install needed to check it.
- The nav now lists all 34 ADRs, all 7 runbooks and `synthetic-data.md`.
- ADR-0033's `Slice:` header said "none yet"; #25 closed it.
- The landing page gained a pointer to the Talos runbook.

Closes #169

## Definition of Done

- [x] Linked Gitea issue (above).
- [x] Failing test committed before the fix — the red commit lists all 31 missing pages.
- [x] Implementation makes the test pass.
- [x] Conventional Commits referencing the issue (`refs #169`).
- [ ] CI green — awaiting the run on this PR (`python3 infra/check-docs-nav.py` passes locally;
      `make lint` also needs the .NET SDK, which CI has).
- [x] `docker compose up` unaffected — docs and `mkdocs.yml` only, plus one `make lint` line.
- [x] Docs updated — that is the change.
- [x] No ADR needed: no dependency, no boundary, no §8 rule touched.
- [x] Not user-visible, so no demo note.

## Notes for reviewers

- The check is a **substring test**, not a YAML parse (there's a `ponytail:` note in the
  script): a page's path either appears in `mkdocs.yml` or it doesn't. That keeps it
  dependency-free — `mkdocs.yml` can't be read by `yaml.safe_load` anyway, it carries a
  `!!python/name:` tag for the mermaid fence. It does not check that an entry *points at a
  file that exists*; mkdocs' `not_found: warn` covers that direction.
- ADR labels in the nav are shortened by hand (`"ADR-0013: Behandel-portal wiring"`), since
  several H1s are a full sentence.

**Known gap, not fixed here:** CLAUDE.md §12 says the site is "published via a Gitea Actions
workflow to Gitea Pages", and no such workflow exists — `mkdocs build` is never run, by CI or
by any make target. Gitea has no built-in Pages, so publishing needs a decision (a
`gitea-pages` server, an artifact, or a static host) rather than a patch. Worth its own issue
if the published site is actually wanted; until then this PR makes the nav correct for whoever
runs `mkdocs serve`.Reviewed-on: #172

docs/architecture/adr-0033-kubernetes-via-one-helm-chart.md

@@ -3,8 +3,8 @@
 - **Status:** Accepted
 - **Date:** 2026-09-04
 - **Deciders:** Respellion engineering
-- **Slice:** _(none yet — raised directly as a deployment-target request; see
-  "Process note" at the end)_
+- **Slice:** #25 (S-24) — raised directly as a deployment-target request and matched to
+  that issue afterwards; see the "Process note" at the end
 
 ## Context
 

docs/index.md

@@ -14,6 +14,8 @@ should teach.
   In Dutch; the strategic framing lives in `Respellion/innovation-lab`.
 - **[Working in Gitea](gitea-workflow.md)** — issues, milestones, branches, PRs.
 - **[CI runbook](runbooks/ci.md)** — the pipeline and the `make ci` local gate.
+- **[Kubernetes on Talos](runbooks/kubernetes-talos.md)** — the second deployment target:
+  one Helm chart, a single-node cluster, and the parts that bite (ADR-0033).
 
 ## Quickstart