fix: 后端代码格式化

backend/src/main/java/com/openisle/dto/MessageNotificationPayload.java

@@ -1,15 +1,15 @@
 package com.openisle.dto;
 
+import java.io.Serializable;
 import lombok.AllArgsConstructor;
 import lombok.Data;
 import lombok.NoArgsConstructor;
 
-import java.io.Serializable;
-
 @Data
 @NoArgsConstructor
 @AllArgsConstructor
 public class MessageNotificationPayload implements Serializable {
-    private String targetUsername;
-    private Object payload;
-}
+
+  private String targetUsername;
+  private Object payload;
+}