fix(infra): bake config into images so compose-smoke passes on CI (refs #30)

Root cause of the compose-smoke failure (found in the runner logs):

  oz-init-1 | CommandError: Yaml file
              `/app/setup_configuration/data.yaml` does not exist.

The ubuntu-latest runner runs the job inside a container, so
`docker compose up` starts the stack as SIBLING containers via the host
daemon. A relative bind mount (./openzaak/setup_configuration) resolves to
a path inside the job container that the daemon can't see, so Docker mounts
an empty dir and the init container can't find data.yaml. The same trap hit
nrc-init (data.yaml), flowable-init (the BPMN) and keycloak (realm import).

Fix: bake the assets into small derived images instead of bind-mounting:
  - infra/openzaak/Dockerfile        -> register-referentie/openzaak:dev
  - infra/opennotificaties/Dockerfile-> register-referentie/opennotificaties:dev
  - infra/keycloak/Dockerfile        -> register-referentie/keycloak:dev
  - flowable-init: build.dockerfile_inline bakes workflows/registratie.bpmn

Base versions stay build args (OPENZAAK_TAG / OPENNOTIFICATIES_TAG), so the
pinning is unchanged. Applied to both the consolidated compose and the
per-service composes, so local Podman and CI use one mechanism — no bind
mounts, no SELinux `:z`, no world-readable requirement.

Verified locally: `podman build` of the OpenZaak and BPMN images produces
the file at the expected in-container path.

Docs: docs/runbooks/gitea-actions-gotchas.md explains the DinD bind-mount
trap and the bake fix; openzaak.md and ci.md point at it.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/runbooks/ci.md

@@ -22,6 +22,12 @@ All `uses:` references are absolute, tag-pinned URLs (`https://github.com/action
 `https://github.com/actions/setup-dotnet@v4`) per CLAUDE.md §8.7 and §15 — Gitea
 Actions resolves them from GitHub.
 
+> **`compose-smoke` runs on a containerized runner.** Workspace bind mounts do
+> **not** reach the sibling containers Compose starts, so config/assets are baked
+> into derived images instead of being mounted. If you add a service that needs a
+> repo file at runtime, bake it — don't bind-mount it. See
+> [gitea-actions-gotchas.md](gitea-actions-gotchas.md).
+
 ## Running CI locally (`make ci`)
 
 Until the runner exists, run the full pipeline yourself before pushing: