test(person): address PR #736 review nits

- AC-3 cascade test: assert an innocent bystander's mention row survives the
  delete, proving the cascade is scoped to the deleted person (Nora).
- Fix integration-test comment: receivers is @ManyToMany(LAZY), not an EAGER
  @ElementCollection (Sara).
- ADR-032: note the @ prefix is kept in the degraded path, stripped in live
  mentions (Leonie).
- Add trailing newline to PersonRepository.java (Felix).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/adr/032-person-delete-db-level-integrity.md

@@ -45,7 +45,9 @@ letters. This is pinned by a non-negotiable document-survival assertion in
   stay thin (`deleteById` + the cascade); `reassignSenderToNull` and `deleteReceiverReferences`
   are deleted.
 - This *fixes* the pre-existing dead-link-on-deleted-person case — it is not a purely
-  invisible refactor.
+  invisible refactor. Note the read renderer strips the `@` prefix when it emits a live
+  mention link, but the degraded (deleted-person) path leaves the literal `@Name` in the
+  block text as-is — the reader sees `@Auguste Raddatz` as plain text, never a dead link.
 - DB cascades run below `AuditService`, so the row-level cleanup is intentionally not
   audit-logged; the person-delete action itself is still logged at the service layer.
 - The V71 FK validation requires cleaning pre-existing orphan mention rows first; the