feat: lecture 강의 삭제시 저장소에서 사진 삭제

backend/src/main/java/com/edufocus/edufocus/lecture/service/LectureServiceImpl.java

@@ -113,6 +113,12 @@ public class LectureServiceImpl implements LectureService {
             return false;
         }
 
+        String image = lecture.getImage();
+        if (image != null) {
+            File file = new File(lecture.getImage());
+            file.delete();
+        }
+
         lectureRepository.deleteById(lectureId);
         return true;
     }