feat(documents): wire archiveBox + archiveFolder through DTO and service update

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

@@ -121,6 +121,23 @@ class DocumentServiceTest {
                 .isInstanceOf(DomainException.class);
     }
 
+    @Test
+    void updateDocument_setsArchiveBoxAndFolder() throws Exception {
+        UUID id = UUID.randomUUID();
+        Document doc = Document.builder().id(id).receivers(new HashSet<>()).tags(new HashSet<>()).build();
+        when(documentRepository.findById(id)).thenReturn(Optional.of(doc));
+        when(documentRepository.save(any())).thenReturn(doc);
+
+        DocumentUpdateDTO dto = new DocumentUpdateDTO();
+        dto.setArchiveBox("K-03");
+        dto.setArchiveFolder("Mappe B");
+
+        documentService.updateDocument(id, dto, null, null);
+
+        assertThat(doc.getArchiveBox()).isEqualTo("K-03");
+        assertThat(doc.getArchiveFolder()).isEqualTo("Mappe B");
+    }
+
     // ─── deleteTagCascading ───────────────────────────────────────────────────
 
     @Test