feat(parser): support // as multi-person separator in parseReceivers

Pre-splits input on "//" before existing logic so each segment is
processed independently through the full pipeline (und/u splitting,
last-name distribution, etc.).

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

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

@@ -149,6 +149,38 @@ class PersonNameParserTest {
         assertThat(result).containsExactlyInAnyOrder("Clara Cram", "Eugenie de Gruyter");
     }
 
+    // --- parseReceivers — // separator ---
+
+    @Test
+    void slashSeparator_twoIndependentFullNames() {
+        assertThat(PersonNameParser.parseReceivers("Charl.Blomquist//Tante Lolly"))
+                .containsExactly("Charl.Blomquist", "Tante Lolly");
+    }
+
+    @Test
+    void slashSeparator_abbreviatedFirstName() {
+        assertThat(PersonNameParser.parseReceivers("Walter de Gruyter//Eugenie de Gruyter"))
+                .containsExactly("Walter de Gruyter", "Eugenie de Gruyter");
+    }
+
+    @Test
+    void slashSeparator_withSpacesAroundSlashes() {
+        assertThat(PersonNameParser.parseReceivers(" Herbert Cram // Eugenie de Gruyter "))
+                .containsExactly("Herbert Cram", "Eugenie de Gruyter");
+    }
+
+    @Test
+    void slashSeparator_segmentContainsUnd() {
+        assertThat(PersonNameParser.parseReceivers("Herbert und Clara Cram//Eugenie de Gruyter"))
+                .containsExactly("Herbert Cram", "Clara Cram", "Eugenie de Gruyter");
+    }
+
+    @Test
+    void slashSeparator_trailingSlash() {
+        assertThat(PersonNameParser.parseReceivers("Herbert Cram//"))
+                .containsExactly("Herbert Cram");
+    }
+
     @Test
     void parseReceivers_returnsEmpty_whenAllPartsAreFamilie() {
         // All parts filtered out → nameParts.isEmpty() = true → return List.of()