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/openzaak/docker-compose.yml

@@ -32,7 +32,12 @@ services:
     networks: [cg]
 
   oz-init:
-    image: docker.io/openzaak/open-zaak:${OPENZAAK_TAG:-1.28.2}
+    build:
+      context: .
+      dockerfile: Dockerfile
+      args:
+        OPENZAAK_TAG: ${OPENZAAK_TAG:-1.28.2}
+    image: register-referentie/openzaak:dev
     environment: &oz-env
       DJANGO_SETTINGS_MODULE: openzaak.conf.docker
       SECRET_KEY: ${OZ_SECRET_KEY:-dev-only-not-for-production}
@@ -55,8 +60,6 @@ services:
       OPENZAAK_SUPERUSER_EMAIL: admin@localhost
       RUN_SETUP_CONFIG: "true"
     command: /setup_configuration.sh
-    volumes:
-      - ./setup_configuration:/app/setup_configuration:ro
     depends_on:
       oz-db:
         condition: service_healthy
@@ -65,7 +68,7 @@ services:
     networks: [cg]
 
   openzaak:
-    image: docker.io/openzaak/open-zaak:${OPENZAAK_TAG:-1.28.2}
+    image: register-referentie/openzaak:dev
     environment: *oz-env
     healthcheck:
       test: ["CMD", "python", "-c", "import requests,sys; sys.exit(0 if requests.head('http://localhost:8000/admin/').status_code in (200,302) else 1)"]
@@ -81,7 +84,7 @@ services:
     networks: [cg]
 
   oz-celery:
-    image: docker.io/openzaak/open-zaak:${OPENZAAK_TAG:-1.28.2}
+    image: register-referentie/openzaak:dev
     environment: *oz-env
     command: /celery_worker.sh
     depends_on: