fix(panel): 备份页轮询服务器状态，立即备份按去向判断并在已有备份或回档时等待，重读失败保留页面

panel/src/i18n/resources/en-US/backups.json

@@ -15,6 +15,7 @@
   "backup_now": "Back up now",
   "backup_in_progress": "Starting backup…",
   "backup_started": "Backup started — its progress shows under recent operations below.",
+  "backup_world_busy": "A backup or restore is already running; back up once it finishes.",
   "backup_requires_stopped": "Stop the server before backing it up.",
   "expires_in": "Expires {{when}}",
   "expired": "Expired",

panel/src/i18n/resources/zh-CN/backups.json

@@ -15,6 +15,7 @@
   "backup_now": "立即备份",
   "backup_in_progress": "正在启动备份……",
   "backup_started": "已开始备份——进度可在下方“最近操作”中查看。",
+  "backup_world_busy": "已有备份或回档在进行，等它结束再备份。",
   "backup_requires_stopped": "备份前需要先停止服务器。",
   "expires_in": "{{when}}过期",
   "expired": "已过期",