CLAP-341 Fix: 완료/종료 상태에서 다른 상태로 변경시 finishedAt null 처리

Author: parkjaehak

src/main/java/clap/server/domain/model/task/Task.java

@@ -71,6 +71,9 @@ public void updateTaskStatus(TaskStatus status) {
         if (status.equals(TaskStatus.COMPLETED)) {
             this.finishedAt = LocalDateTime.now();
         }
+        if (this.taskStatus == TaskStatus.TERMINATED || this.taskStatus == TaskStatus.COMPLETED) {
+            this.finishedAt = null;
+        }
         this.taskStatus = status;
     }