Adds the JourneyItemDocumentDeleteListener component and the DocumentDeletingEvent edge (documentSvc -> listener) to the supporting-domains l3 diagram. This is the first event-driven edge in the backend; the diagram must make that in-process coupling visible per the doc-currency rule. Addresses @markus review (blocker) on PR #806. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>