feat(workflow): diploma-eligibility DMN routes foreign diplomas via CBGV-advies (S-13, closes #14) (#101)

## What & why

S-13: a diploma's origin decides its route. A **DMN** (`diploma-eligibility`) is evaluated inline by
the registratie process as a **`businessRuleTask`**; an exclusive gateway routes a **foreign**
(Buitenlands) diploma through a new **CBGVAdvies** user task before `Beoordelen`, a **domestic** one
straight there (PRD flow 4). The domain's only new job is carrying the diploma origin and passing it
as a process start variable.

Chose **Option B (DMN in the BPMN)** over the issue's literal "evaluated by the Domain Service via
Workflow Client" wording — keeps the decision a first-class workflow artefact and §8.2 clean.
Rationale in **ADR-0016** (proposal #100); noted on this issue.

Closes #14

## Definition of Done

- [x] Linked Gitea issue (above).
- [x] Failing test committed before the implementation.
- [x] Implementation makes the test pass.
- [x] Conventional Commits referencing the issue (`refs #14`).
- [ ] CI green — all Gitea Actions jobs.
- [x] `docker compose up` from a fresh clone reaches green health checks within 3 minutes (additive; DMN deployed by flowable-init).
- [x] Docs updated (ADR-0016, demo note).
- [x] ADR added (`docs/architecture/adr-0016-diploma-eligibility-dmn.md`).
- [x] Demo note in `docs/demo-script.md`.

## How it was built (TDD)

- **Domain**: `DiplomaOrigin` on the aggregate + submit command; threaded through the process-start port so the Workflow Client emits a `diplomaOrigin` start variable. Red → green.
- **DMN + BPMN**: `workflows/diploma-eligibility.dmn` (origin → route); `businessRuleTask` + exclusive gateway + `CBGVAdvies` user task in `registratie.bpmn`; DMN deployed to Flowable's DMN engine by `flowable-init`.
- **Both paths**: `Een diploma op herkomst routeren` acceptance scenarios (origin carried into the process) + unit tests; verify-domain drives a foreign registration through CBGVAdvies→Beoordelen and the domestic one straight to Beoordelen — exercising both DMN branches live.

## Notes for reviewers

- Deviation from the issue's Option-A wording is deliberate and recorded (ADR-0016); the outcome is unchanged.
- The self-service eIDAS→foreign wiring is out of scope here (this slice is area:domain + area:workflow); the domain submit accepts an optional `diplomaOrigin` so the foreign path is drivable.
- Local green: domain unit 109, acceptance 15, `dotnet format`, Release build (0 errors), **domain mutation 95.39%** (break 90). The DMN/`businessRuleTask` REST wiring is CI-verified on verify-stack (no local full-stack run here).

Reviewed-on: #101

infra/docker-compose.yml

@@ -259,19 +259,30 @@ services:
   flowable-init:
     image: docker.io/curlimages/curl:latest
     restart: "no"
-    # registratie.bpmn is streamed into this external volume by infra/seed-config.sh.
+    # registratie.bpmn + diploma-eligibility.dmn are streamed into this external volume by
+    # infra/seed-config.sh.
     volumes:
       - fl-bpmn:/work:ro
     command:
       - sh
       - -c
       - |
-        base=http://flowable-rest:8080/flowable-rest/service/repository/deployments
-        until curl -sf -u rest-admin:test "$$base" >/dev/null 2>&1; do echo "waiting for flowable-rest..."; sleep 3; done
-        if curl -s -u rest-admin:test "$$base?name=registratie" | grep -q '"name":"registratie"'; then
-          echo "registratie already deployed; skip"
+        svc=http://flowable-rest:8080/flowable-rest/service/repository/deployments
+        dmn=http://flowable-rest:8080/flowable-rest/dmn-api/dmn-repository/deployments
+        until curl -sf -u rest-admin:test "$$svc" >/dev/null 2>&1; do echo "waiting for flowable-rest..."; sleep 3; done
+        # Deploy the DMN to the DMN engine and the BPMN to the process engine as SEPARATE deployments:
+        # flowable-rest does NOT cascade a .dmn bundled in a process .bar into the DMN engine, so the DMN
+        # must go via dmn-api. The process's DMN service task then resolves the decision across deployments
+        # by key (S-13, ADR-0016). Both steps are idempotent (skip if already deployed).
+        if curl -s -u rest-admin:test "$$dmn" | grep -q '"name":"diploma-eligibility.dmn"'; then
+          echo "diploma-eligibility DMN already deployed; skip"
         else
-          curl -sf -u rest-admin:test -F 'file=@/work/registratie.bpmn;filename=registratie.bpmn' "$$base" >/dev/null && echo "deployed registratie"
+          curl -sf -u rest-admin:test -F 'file=@/work/diploma-eligibility.dmn;filename=diploma-eligibility.dmn' "$$dmn" >/dev/null && echo "deployed diploma-eligibility DMN"
+        fi
+        if curl -s -u rest-admin:test "$$svc?name=registratie" | grep -q '"name":"registratie"'; then
+          echo "registratie BPMN already deployed; skip"
+        else
+          curl -sf -u rest-admin:test -F 'file=@/work/registratie.bpmn;filename=registratie.bpmn' "$$svc" >/dev/null && echo "deployed registratie BPMN"
         fi
     depends_on:
       flowable-rest: