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>

infra/flowable/docker-compose.yml

@@ -38,10 +38,16 @@ services:
   # Deploys workflows/registratie.bpmn via the REST API once flowable-rest is up.
   # Idempotent: skips if a deployment named "registratie" already exists.
   flowable-init:
-    image: docker.io/curlimages/curl:latest
+    # The BPMN is baked into a tiny curl image (build context = repo-root
+    # workflows/) instead of bind-mounted, so the deploy works on Gitea's
+    # containerized runner too. See docs/runbooks/gitea-actions-gotchas.md.
+    build:
+      context: ../../workflows
+      dockerfile_inline: |
+        FROM docker.io/curlimages/curl:latest
+        COPY registratie.bpmn /work/registratie.bpmn
+    image: register-referentie/flowable-init:dev
     restart: "no"
-    volumes:
-      - ../../workflows/registratie.bpmn:/work/registratie.bpmn:ro,z
     command:
       - sh
       - -c