feat: 읽음 조회 API 추가

src/main/java/com/feesh/domain/notification/controller/NotificationController.java

@@ -10,6 +10,7 @@
 import org.springframework.web.bind.annotation.RestController;
 
 import java.util.List;
+import java.util.Map;
 
 @RestController
 @RequestMapping("/alarm")
@@ -29,4 +30,11 @@ public ResponseEntity<List<NotificationResponseDto>> getLikeAlarms() {
         Long userId = SecurityUtil.getCurrentUserId();
         return ResponseEntity.ok(notificationService.getLikeAlarms(userId));
     }
+
+    @GetMapping("/unread-count")
+    public ResponseEntity<Map<String, Long>> getUnreadCount() {
+        Long userId = SecurityUtil.getCurrentUserId();
+        long count = notificationService.getUnreadCount(userId);
+        return ResponseEntity.ok(Map.of("unreadCount", count));
+    }
 }

src/main/java/com/feesh/domain/notification/repository/NotificationRepository.java

@@ -13,6 +13,8 @@ List<Notification> findByReceiverIdAndTypeOrderByCreatedAtDesc(
             NotificationType type
     );
 
+    long countByReceiverIdAndIsReadFalse(Long receiverId);
+
     void deleteAllByReceiverId(Long receiverId);
 
     void deleteAllBySenderId(Long senderId);

src/main/java/com/feesh/domain/notification/service/NotificationService.java

@@ -27,20 +27,38 @@ public class NotificationService {
     private final UserRepository userRepository;
     private final CommentRepository commentRepository;
 
+    @Transactional
     public List<NotificationResponseDto> getCommentAlarms(Long userId) {
         List<Notification> notifications = notificationRepository
                 .findByReceiverIdAndTypeOrderByCreatedAtDesc(userId, NotificationType.COMMENT);
 
+        markAsRead(notifications);
+
         return toResponseDtos(notifications);
     }
 
+    @Transactional
     public List<NotificationResponseDto> getLikeAlarms(Long userId) {
         List<Notification> notifications = notificationRepository
                 .findByReceiverIdAndTypeOrderByCreatedAtDesc(userId, NotificationType.LIKE);
 
+        markAsRead(notifications);
+
         return toResponseDtos(notifications);
     }
 
+    // 헤더에 표시할 안 읽은 알림 개수
+    public long getUnreadCount(Long userId) {
+        return notificationRepository.countByReceiverIdAndIsReadFalse(userId);
+    }
+
+    // 조회한 알림들 읽음 처리 (더티체킹으로 자동 반영)
+    private void markAsRead(List<Notification> notifications) {
+        notifications.stream()
+                .filter(notification -> !notification.isRead())
+                .forEach(Notification::markAsRead);
+    }
+
     // 알림 목록의 senderId, commentId를 모아 각각 한 번에 조회한 뒤 DTO로 변환 (N+1 방지)
     private List<NotificationResponseDto> toResponseDtos(List<Notification> notifications) {
         List<Long> senderIds = notifications.stream()