test(transcription): all in-block mention occurrences rewrite on rename

When the same person is mentioned twice in one block, both substrings flip
to the new display name. String.replace(String, String) is documented to
replace every occurrence, but a future regex-based refactor or a typo could
silently regress to first-match-only — this test guards against that.

Refs #362

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

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

@@ -122,6 +122,27 @@ class PersonMentionPropagationListenerTest {
                         org.assertj.core.groups.Tuple.tuple(hansId, "Hans Schmidt"));
     }
 
+    @Test
+    void rewritesAllOccurrences_whenSameMentionAppearsTwiceInBlock() {
+        UUID personId = savedPersonId("Auguste", "Raddatz");
+        TranscriptionBlock saved = saveBlock(
+                "Heute hat @Auguste Raddatz geschrieben, dann hat @Auguste Raddatz nochmal geschrieben.",
+                List.of(new PersonMention(personId, "Auguste Raddatz")));
+        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("Heute hat @Augusta Raddatz geschrieben, dann hat @Augusta Raddatz nochmal geschrieben.");
+        assertThat(reloaded.getMentionedPersons())
+                .extracting(PersonMention::getDisplayName)
+                .containsExactly("Augusta Raddatz");
+    }
+
     @Test
     void leavesUnrelatedBlockUntouched_whenNoSidecarReferencesPerson() {
         UUID personId = savedPersonId("Auguste", "Raddatz");