refactor(infra): use upstream images verbatim, seed config via docker cp (refs #30)

Drops the inline-build images for the upstream services. The compose now
references the published images directly (openzaak/open-zaak,
openzaak/open-notificaties, keycloak, curl, flowable-rest) with no build for
them, and the config they need is streamed into external named volumes by
infra/seed-config.sh:

  rr-oz-config  -> oz-init     /app/setup_configuration   (data.yaml)
  rr-kc-realms  -> keycloak    /opt/keycloak/data/import   (realm exports)
  rr-fl-bpmn    -> flowable-init /work                     (registratie.bpmn)

How: the seeder creates each volume, `docker create`s a throwaway helper that
mounts it, `docker cp`s the files in, and removes it. docker cp streams over the
Docker API, so it works in Docker-in-Docker (the CI runner) where bind mounts
mount empty. It uses plain `docker create`/`cp` — NOT `docker compose create`,
which podman-compose (local dev) lacks. `external: true` fixed names keep the
volumes identical across docker compose and podman-compose.

Consequence: bare `docker compose up` no longer self-seeds, so use `make up`
(seeds then starts). Every `*-up` target seeds first; `*-down` removes the
external volume. acl/bff are still built (they're our apps, not upstream images).

Verified end-to-end on podman-compose: `make keycloak-up` seeds rr-kc-realms,
the upstream Keycloak mounts it, and --import-realm imports all four realms
(digid realm returns 200). Seeder runs in ~2s.

Docs updated: gitea-actions-gotchas.md, ci.md, openzaak.md.

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

infra/docker-compose.yml

@@ -47,17 +47,7 @@ services:
     networks: [cg]
 
   oz-init:
-    # Derived image: base OpenZaak + the setup_configuration YAML baked in. We use
-    # an inline Dockerfile (not a separate file, not a bind mount) because bind
-    # mounts don't reach sibling containers on the containerized CI runner.
-    # The ${OPENZAAK_TAG} below is interpolated by Compose. See
-    # docs/runbooks/gitea-actions-gotchas.md.
-    build:
-      context: ./openzaak
-      dockerfile_inline: |
-        FROM docker.io/openzaak/open-zaak:${OPENZAAK_TAG:-1.28.2}
-        COPY setup_configuration /app/setup_configuration
-    image: register-referentie/openzaak:dev
+    image: docker.io/openzaak/open-zaak:${OPENZAAK_TAG:-1.28.2}
     environment: &oz-env
       DJANGO_SETTINGS_MODULE: openzaak.conf.docker
       SECRET_KEY: ${OZ_SECRET_KEY:-dev-only-not-for-production}
@@ -78,6 +68,10 @@ services:
       OPENZAAK_SUPERUSER_EMAIL: admin@localhost
       RUN_SETUP_CONFIG: "true"
     command: /setup_configuration.sh
+    # data.yaml is streamed into this external volume by infra/seed-config.sh
+    # before start (bind mounts don't reach sibling containers on the CI runner).
+    volumes:
+      - oz-config:/app/setup_configuration:ro
     depends_on:
       oz-db:
         condition: service_healthy
@@ -86,7 +80,7 @@ services:
     networks: [cg]
 
   openzaak:
-    image: register-referentie/openzaak:dev
+    image: docker.io/openzaak/open-zaak:${OPENZAAK_TAG:-1.28.2}
     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)"]
@@ -102,7 +96,7 @@ services:
     networks: [cg]
 
   oz-celery:
-    image: register-referentie/openzaak:dev
+    image: docker.io/openzaak/open-zaak:${OPENZAAK_TAG:-1.28.2}
     environment: *oz-env
     command: /celery_worker.sh
     depends_on:
@@ -193,14 +187,7 @@ services:
 
   # ── Keycloak (S-02) ──────────────────────────────────────────────────────
   keycloak:
-    # Derived image: base Keycloak + the realm exports baked into the import dir
-    # (inline Dockerfile, no bind mount — see docs/runbooks/gitea-actions-gotchas.md).
-    build:
-      context: ./keycloak
-      dockerfile_inline: |
-        FROM quay.io/keycloak/keycloak:26.1
-        COPY realms /opt/keycloak/data/import
-    image: register-referentie/keycloak:dev
+    image: quay.io/keycloak/keycloak:26.1
     command: ["start-dev", "--import-realm"]
     environment:
       KC_BOOTSTRAP_ADMIN_USERNAME: admin
@@ -211,6 +198,9 @@ services:
       KC_HTTP_ENABLED: "true"
     ports:
       - "8180:8080"
+    # realm exports are streamed into this external volume by infra/seed-config.sh.
+    volumes:
+      - kc-realms:/opt/keycloak/data/import:ro
     networks: [cg]
 
   # ── Flowable (S-03) ──────────────────────────────────────────────────────
@@ -244,16 +234,11 @@ services:
     networks: [cg]
 
   flowable-init:
-    # 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
+    image: docker.io/curlimages/curl:latest
     restart: "no"
+    # registratie.bpmn is streamed into this external volume by infra/seed-config.sh.
+    volumes:
+      - fl-bpmn:/work:ro
     command:
       - sh
       - -c
@@ -318,6 +303,18 @@ volumes:
   oz-db:
   nrc-db:
   flowable-db:
+  # Config volumes — created and populated out-of-band by infra/seed-config.sh
+  # (docker cp), because bind mounts don't reach sibling containers on the CI
+  # runner. `external` keeps the names deterministic; the seed step manages them.
+  oz-config:
+    external: true
+    name: rr-oz-config
+  kc-realms:
+    external: true
+    name: rr-kc-realms
+  fl-bpmn:
+    external: true
+    name: rr-fl-bpmn
 
 networks:
   cg: