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>

workflows/registratie.bpmn

@@ -22,9 +22,9 @@
        (BeoordelingEscaleren); the Workflow Client reassigns the still-open Beoordelen task from the
        behandelaar group to teamlead (ADR-0015). The Beoordelen task stays open throughout — the timer
        only changes who may claim it.
-       S-13 adds diploma-eligibility routing: between OpenZaakAanmaken and Beoordelen a DMN
-       businessRuleTask evaluates the `diploma-eligibility` decision on the diplomaOrigin start
-       variable; an exclusive gateway routes a foreign diploma through the CBGV-advies user task
+       S-13 adds diploma-eligibility routing: between OpenZaakAanmaken and Beoordelen a DMN service
+       task (flowable:type="dmn") evaluates the `diploma-eligibility` decision on the diplomaOrigin
+       start variable; an exclusive gateway routes a foreign diploma through the CBGV-advies user task
        before Beoordelen, a domestic one straight there (ADR-0016). -->
   <message id="Message_Ingetrokken" name="RegistratieIngetrokken"/>
 
@@ -40,17 +40,19 @@
 
     <sequenceFlow id="flow2" sourceRef="OpenZaakAanmaken" targetRef="DiplomaEligibiliteit"/>
 
-    <!-- S-13: evaluate the diploma-eligibility DMN inline (ADR-0016). Flowable runs the deployed
-         `diploma-eligibility` decision against the diplomaOrigin start variable and sets the `route`
-         output as a process variable. The gateway then routes a foreign diploma through CBGV-advies,
-         a domestic one straight to Beoordelen. -->
-    <businessRuleTask id="DiplomaEligibiliteit" name="Diploma-eligibiliteit bepalen" flowable:type="dmn">
+    <!-- S-13: evaluate the diploma-eligibility DMN inline (ADR-0016). A Flowable DMN service task
+         (flowable:type="dmn" — NOT a businessRuleTask, whose default implementation is the legacy
+         Drools/KIE one that flowable-rest does not bundle) runs the deployed `diploma-eligibility`
+         decision against the diplomaOrigin start variable and sets the `route` output as a process
+         variable. The gateway then routes a foreign diploma through CBGV-advies, a domestic one
+         straight to Beoordelen. -->
+    <serviceTask id="DiplomaEligibiliteit" name="Diploma-eligibiliteit bepalen" flowable:type="dmn">
       <extensionElements>
         <flowable:field name="decisionTableReferenceKey">
           <flowable:string><![CDATA[diploma-eligibility]]></flowable:string>
         </flowable:field>
       </extensionElements>
-    </businessRuleTask>
+    </serviceTask>
 
     <sequenceFlow id="flow2a" sourceRef="DiplomaEligibiliteit" targetRef="RouteOpDiploma"/>