fix(docs): drop the link out of docs_dir so the strict build passes (refs #173)

MkDocs can't resolve links outside docs/, so the stryker-config.json path is
now plain code. The CI runbook lists the new docs job.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/runbooks/ci.md

@@ -19,6 +19,7 @@ and CI cannot drift:
 | `build` | `make build` → `dotnet build … -c Release` | .NET 10 SDK |
 | `unit` | `make unit` → `dotnet test … -c Release --filter "Category!=Integration"` | .NET 10 SDK |
 | `frontend` | `make frontend` → Nx lint/test/build for the four portals | pnpm + Node |
+| `docs` | `make docs` → `mkdocs build --strict` in a pinned venv (fails on a broken link or nav entry; the site is not published yet, #173) | Python 3 |
 | `k8s` | `make k8s-lint` (render + schema-check the Helm chart) → `make k8s-drift` (chart still describes the same stack as `infra/docker-compose.yml`) | pinned `helm` binary + `docker compose` |
 | `mutation` | `make mutation` → `dotnet tool restore` → `dotnet stryker` (ACL); uploads the HTML report as an artifact | .NET 10 SDK |
 | `verify-stack` | **push to `main` only, skipped on PRs** (#182) — the single live-stack stage — steps: `make verify-up` (full stack up + health, the DoD smoke) → `make verify-acl` (ACL ↔ OpenZaak) → `make verify-nrc` (OpenZaak → NRC delivery) → `make down` | container engine + egress (base images, nuget, `selectielijst.openzaak.nl`) |
@@ -57,7 +58,7 @@ dotnet tool (`.config/dotnet-tools.json`), so it runs identically locally and in
 make mutation     # dotnet tool restore + dotnet stryker on the ACL
 ```
 
-Config lives in [`services/acl/stryker-config.json`](../../services/acl/stryker-config.json).
+Config lives in `services/acl/stryker-config.json`.
 It runs in **solution mode** against `Acl.slnx`, mutating the two projects under test
 (`Acl.Application`, `Acl.Infrastructure`); `Acl.Api` has no tests and is skipped.