fix(workflow): use a DMN service task, not businessRuleTask (S-13, refs #14)

flowable-rest's businessRuleTask parse handler binds the legacy Drools/KIE
implementation (NoClassDefFoundError: org.kie.api...AgendaFilter at deploy time),
so registratie.bpmn failed to deploy and flowable-init exited 22. Flowable's
supported inline-DMN construct is a serviceTask with flowable:type="dmn" — switch
to it. The DMN cross-deploy via the process repository (previous commit) was fine;
this was the BPMN parse. Docs/comments updated to match.

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

docs/demo-script.md

@@ -346,7 +346,7 @@ candidate group behandelaar → teamlead (§8.2).
 
 ## S-13 — Diploma-eligibility: foreign diplomas route through CBGV-advies (#14, ADR-0016)
 
-A registration's diploma origin decides its route. A DMN `businessRuleTask` in the registratie
+A registration's diploma origin decides its route. A DMN service task in the registratie
 process evaluates the `diploma-eligibility` decision on the `diplomaOrigin` start variable: a
 **foreign** (Buitenlands) diploma is routed through an extra **CBGV-advies** user task before
 beoordeling; a **domestic** (Binnenlands) one goes straight to beoordeling. The decision lives in the
@@ -376,7 +376,7 @@ curl -s -u rest-admin:test -X POST "$FL/runtime/tasks/$TID" \
 ```
 
 **The path:** domain sets the `diplomaOrigin` start variable → registratie process DMN
-`businessRuleTask` sets `route` → exclusive gateway → foreign: `CBGVAdvies` user task → `Beoordelen`;
+DMN service task sets `route` → exclusive gateway → foreign: `CBGVAdvies` user task → `Beoordelen`;
 domestic: `Beoordelen` directly (§8.2, ADR-0016).
 
 > The domestic/foreign paths are covered by the `Een diploma op herkomst routeren` acceptance