fix: retain only recent WebDAV backups

handlers/settings.go

@@ -78,10 +78,38 @@ func RunCloudBackup(c *gin.Context) {
 
 	// 清理本地旧备份，保留最近5份
 	config.CleanOldBackups(5)
+	if err := cleanOldRemoteBackups(client, 5); err != nil {
+		log.Printf("云端旧备份清理失败: %v", err)
+	}
 
 	c.JSON(http.StatusOK, Response{Success: true, Message: "备份成功: " + remoteName})
 }
 
+// cleanOldRemoteBackups 清理 WebDAV 上的旧备份，仅保留最近 keep 份。
+func cleanOldRemoteBackups(client *config.WebDAVClient, keep int) error {
+	if keep < 1 {
+		keep = 1
+	}
+	files, err := client.List()
+	if err != nil {
+		return err
+	}
+	if len(files) <= keep {
+		return nil
+	}
+	var firstErr error
+	for _, file := range files[keep:] {
+		if err := client.Delete(file.Name); err != nil {
+			if firstErr == nil {
+				firstErr = fmt.Errorf("删除 %s: %w", file.Name, err)
+			}
+			continue
+		}
+		log.Printf("已清理云端旧备份: %s", file.Name)
+	}
+	return firstErr
+}
+
 // ListCloudBackups 列出云端备份
 func ListCloudBackups(c *gin.Context) {
 	client, err := getWebDAVClient()
@@ -217,5 +245,8 @@ func doAutoBackup() {
 	}
 
 	config.CleanOldBackups(5)
+	if err := cleanOldRemoteBackups(client, 5); err != nil {
+		log.Printf("云端旧备份清理失败: %v", err)
+	}
 	log.Printf("自动备份成功: %s", remoteName)
 }