refactor(test): rename test to reflect actual invariant (displayName fields unchanged)

updatePerson_doesNotPublishEvent_whenOnlyAliasChanges implied that alias is
processed by updatePerson — it isn't. The invariant is that the event is
suppressed when title/firstName/lastName are all unchanged regardless of
which non-displayName field changed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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

@@ -284,7 +284,7 @@ class PersonServiceTest {
     }
 
     @Test
-    void updatePerson_doesNotPublishEvent_whenOnlyAliasChanges() {
+    void updatePerson_doesNotPublishEvent_whenDisplayNameFieldsUnchanged() {
         UUID id = UUID.randomUUID();
         Person existing = Person.builder()
                 .id(id).firstName("Auguste").lastName("Raddatz")