fix(parser): preserve annotation parens for single-person inputs

Move paren extraction in parseReceivers() after the multi-separator
check so single-person entries like "Clara de Gruyter(*1871)" keep
their parens intact for split()'s annotation extraction. Multi-person
entries like "Hedi und Tutu (Gruber)" still use parens as shared
last-name override.

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

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

@@ -24,6 +24,18 @@ class PersonNameParserTest {
                 .containsExactly("Eugenie de Gruyter");
     }
 
+    @Test
+    void singlePerson_annotationParenPreserved() {
+        assertThat(PersonNameParser.parseReceivers("Clara de Gruyter(*1871)"))
+                .containsExactly("Clara de Gruyter(*1871)");
+    }
+
+    @Test
+    void singlePerson_nicknameParenPreserved() {
+        assertThat(PersonNameParser.parseReceivers("Gertrud D.(Tuttu)"))
+                .containsExactly("Gertrud D.(Tuttu)");
+    }
+
     @Test
     void gebAnnotation_noDot_multiWord_stripped() {
         assertThat(PersonNameParser.parseReceivers("Ella Dieckmann, geb de Gruyter"))