refactor(infra): bake config via dockerfile_inline, drop Dockerfile files (refs #30)

Replaces the three standalone Dockerfiles (openzaak, opennotificaties,
keycloak) with `build.dockerfile_inline` recipes in the compose files, so the
config bake has no separate Dockerfile artifacts to maintain. Behaviour is
identical: each derived image still COPYies its config in.

- oz-init / keycloak / flowable-init: 2-line inline Dockerfiles.
- Open Notificaties needs no bake at all now — nrc-init runs migrations only,
  so all NRC services use the plain base image (removes a whole derived image).

Why dockerfile_inline and not `docker cp` into named volumes: docker cp avoids
images entirely but needs `docker compose create`, which podman-compose (the
local dev runtime) does not implement — it would break `make openzaak-up` etc.
locally. dockerfile_inline works on both podman-compose and the CI runner
(verified both: oz-init + keycloak inline builds locally; flowable-init inline
has been green on CI since run 27).

Docs updated: gitea-actions-gotchas.md and openzaak.md.

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

docs/runbooks/gitea-actions-gotchas.md

@@ -40,18 +40,24 @@ exposed it.
 
 **Fix: bake assets into derived images instead of bind-mounting them.** Anything
 a Compose service needs at runtime that lives in the repo is `COPY`-ed into a
-small derived image, so it is present regardless of where the daemon runs:
+small derived image, so it is present regardless of where the daemon runs. We use
+**`build.dockerfile_inline`** — the 2-line recipe lives in the compose file, so
+there are no standalone `Dockerfile` artifacts to maintain:
 
-| Asset | Derived image | Dockerfile |
+| Asset | Derived image | Built by |
 |---|---|---|
-| OpenZaak `setup_configuration/data.yaml` | `register-referentie/openzaak:dev` | `infra/openzaak/Dockerfile` |
-| Open Notificaties `setup_configuration/data.yaml` | `register-referentie/opennotificaties:dev` | `infra/opennotificaties/Dockerfile` |
-| Keycloak realm exports | `register-referentie/keycloak:dev` | `infra/keycloak/Dockerfile` |
-| `workflows/registratie.bpmn` | `register-referentie/flowable-init:dev` | `build.dockerfile_inline` in the compose files |
+| OpenZaak `setup_configuration/data.yaml` | `register-referentie/openzaak:dev` | `oz-init` `dockerfile_inline` |
+| Keycloak realm exports | `register-referentie/keycloak:dev` | `keycloak` `dockerfile_inline` |
+| `workflows/registratie.bpmn` | `register-referentie/flowable-init:dev` | `flowable-init` `dockerfile_inline` |
 
-The base image tag stays a build `arg` (`OPENZAAK_TAG`, `OPENNOTIFICATIES_TAG`)
-so version pinning is unchanged. The three `*-init`/web/celery services that share
-a base now share one built image tag, so the bake happens once per `up --build`.
+The base image tag is interpolated by Compose (`${OPENZAAK_TAG}`) so pinning is
+unchanged. OpenZaak's `openzaak`/`oz-celery` reuse the one image `oz-init` builds.
+Open Notificaties needs **no** bake — `nrc-init` runs migrations only, so all NRC
+services use the plain base image.
+
+`dockerfile_inline` works on both the CI runner (docker compose) and local
+**podman-compose**, unlike `docker cp`-into-volumes (which needs `docker compose
+create`, a subcommand podman-compose lacks).
 
 **Why not the alternatives.**
 

docs/runbooks/openzaak.md

@@ -74,6 +74,6 @@ The Makefile auto-points `DOCKER_HOST` at the Podman socket when it exists, so t
 - **Image tag.** Pinned to `openzaak/open-zaak:1.28.2` via `${OPENZAAK_TAG}` (bump
   deliberately, not via `:latest`).
 - **Config is baked, not mounted.** `setup_configuration/data.yaml` is `COPY`-ed into
-  a derived image (`infra/openzaak/Dockerfile`) rather than bind-mounted, so the
-  init container finds it on Gitea's containerized CI runner too. See
-  [gitea-actions-gotchas.md](gitea-actions-gotchas.md).
+  a derived image via `oz-init`'s inline Dockerfile (`build.dockerfile_inline` in
+  the compose) rather than bind-mounted, so the init container finds it on Gitea's
+  containerized CI runner too. See [gitea-actions-gotchas.md](gitea-actions-gotchas.md).