test(transcription): listener no-op when no block references the renamed person

Save a block with no sidecar entries, fire a rename event for an unrelated
person, and assert the block reloads with its original text and empty
sidecar. Confirms findByMentionedPersons_PersonId returns an empty list and
the saveAll path does not accidentally touch unrelated rows.

Refs #362

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/src/test/java/org/raddatz/familienarchiv/service/PersonMentionPropagationListenerTest.java

@@ -95,4 +95,22 @@ class PersonMentionPropagationListenerTest {
                 .extracting(PersonMention::getDisplayName)
                 .containsExactly("Augusta Raddatz");
     }
+
+    @Test
+    void leavesUnrelatedBlockUntouched_whenNoSidecarReferencesPerson() {
+        UUID personId = savedPersonId("Auguste", "Raddatz");
+        TranscriptionBlock saved = saveBlock(
+                "Plain text without any mentions.",
+                List.of());
+        em.clear();
+
+        listener.onPersonDisplayNameChanged(
+                new PersonDisplayNameChangedEvent(personId, "Auguste Raddatz", "Augusta Raddatz"));
+        blockRepository.flush();
+        em.clear();
+
+        TranscriptionBlock reloaded = blockRepository.findById(saved.getId()).orElseThrow();
+        assertThat(reloaded.getText()).isEqualTo("Plain text without any mentions.");
+        assertThat(reloaded.getMentionedPersons()).isEmpty();
+    }
 }