feat(backend): trigger reply notifications from CommentService

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

backend/src/main/java/org/raddatz/familienarchiv/service/CommentService.java

@@ -17,6 +17,7 @@ import java.util.UUID;
 public class CommentService {
 
     private final CommentRepository commentRepository;
+    private final NotificationService notificationService;
 
     public List<DocumentComment> getCommentsForDocument(UUID documentId) {
         List<DocumentComment> roots =
@@ -60,7 +61,9 @@ public class CommentService {
                 .authorId(author.getId())
                 .authorName(resolveAuthorName(author))
                 .build();
-        return commentRepository.save(reply);
+        DocumentComment saved = commentRepository.save(reply);
+        notificationService.notifyReply(saved, root);
+        return saved;
     }
 
     @Transactional

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

@@ -20,6 +20,7 @@ import java.util.UUID;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
@@ -30,6 +31,7 @@ import static org.springframework.http.HttpStatus.NOT_FOUND;
 class CommentServiceTest {
 
     @Mock CommentRepository commentRepository;
+    @Mock NotificationService notificationService;
     @InjectMocks CommentService commentService;
 
     // ─── postComment ──────────────────────────────────────────────────────────
@@ -119,6 +121,25 @@ class CommentServiceTest {
         assertThat(result.getParentId()).isEqualTo(rootId);
     }
 
+    @Test
+    void replyToComment_triggersNotification_afterSave() {
+        UUID docId = UUID.randomUUID();
+        UUID rootId = UUID.randomUUID();
+        AppUser author = AppUser.builder().id(UUID.randomUUID()).username("anna").build();
+
+        DocumentComment root = DocumentComment.builder()
+                .id(rootId).documentId(docId).parentId(null).content("Root").authorName("Hans").build();
+        DocumentComment saved = DocumentComment.builder()
+                .id(UUID.randomUUID()).documentId(docId).parentId(rootId).content("Reply").authorName("anna").build();
+
+        when(commentRepository.findById(rootId)).thenReturn(Optional.of(root));
+        when(commentRepository.save(any())).thenReturn(saved);
+
+        commentService.replyToComment(docId, rootId, "Reply", author);
+
+        verify(notificationService).notifyReply(eq(saved), eq(root));
+    }
+
     // ─── editComment ──────────────────────────────────────────────────────────
 
     @Test