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>

infra/flowable/docker-compose.yml

@@ -51,7 +51,7 @@ services:
         until curl -sf -u rest-admin:test "$$base" >/dev/null 2>&1; do echo "waiting for flowable-rest..."; sleep 3; done
         # Deploy the diploma-eligibility DMN via the process repository: the flowable-rest image embeds
         # the DMN engine but does not expose the dmn-api app, so the process deployment cross-deploys the
-        # .dmn resource to the DMN engine, where the registratie businessRuleTask resolves it by key
+        # .dmn resource to the DMN engine, where the registratie DMN service task resolves it by key
         # (S-13, ADR-0016).
         if curl -s -u rest-admin:test "$$base?name=diploma-eligibility" | grep -q '"name":"diploma-eligibility"'; then
           echo "diploma-eligibility already deployed; skip"