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/seed-config.sh

@@ -35,12 +35,21 @@ populate() {  # volume  source(file or dir/.)
 
 [ "$#" -gt 0 ] || { echo "usage: seed-config.sh <oz|nrc|kc|fl> ..." >&2; exit 2; }
 
+# The registratie process (BPMN) and its diploma-eligibility DMN are deployed as SEPARATE Flowable
+# deployments — the process engine and the DMN engine each own theirs (S-13, ADR-0016). flowable-rest
+# does not cascade a .dmn bundled in a process .bar into the DMN engine, so we seed both raw files and
+# let flowable-init deploy each via its own REST app. We stage them in a temp dir and copy its contents.
+stage_flowable_workflows() {
+  local dir="$1"
+  cp "$here/../workflows/registratie.bpmn" "$here/../workflows/diploma-eligibility.dmn" "$dir/"
+}
+
 for key in "$@"; do
   case "$key" in
     oz) populate rr-oz-config "$here/openzaak/setup_configuration/." ;;
     nrc) populate rr-nrc-config "$here/opennotificaties/setup_configuration/." ;;
     kc) populate rr-kc-realms "$here/keycloak/realms/." ;;
-    fl) populate rr-fl-bpmn  "$here/../workflows/registratie.bpmn" ;;
+    fl) d="$(mktemp -d)"; stage_flowable_workflows "$d"; populate rr-fl-bpmn "$d/." ;;
     *)  echo "unknown seed key: $key" >&2; exit 2 ;;
   esac
 done