feat: local backup (#5054)

* feat: local backup

* refactor(backup): make local backup helpers synchronous and clean up redundant checks

- Converted local backup helpers to synchronous functions to remove unused async warnings and align command signatures.
- Updated list/delete/export commands to call the sync feature functions directly without awaits while preserving behavior.
- Simplified destination directory creation to always ensure parent folders exist without redundant checks, satisfying Clippy.

src/locales/zh.json

@@ -387,7 +387,7 @@
   "toggle_tun_mode": "打开/关闭 TUN 模式",
   "entry_lightweight_mode": "进入轻量模式",
   "Backup Setting": "备份设置",
-  "Backup Setting Info": "支持 WebDAV 备份配置文件",
+  "Backup Setting Info": "支持本地或 WebDAV 方式备份配置文件",
   "Runtime Config": "当前配置",
   "Open Conf Dir": "配置目录",
   "Open Conf Dir Info": "如果软件运行异常，!备份!并删除此文件夹下的所有文件，重启软件",
@@ -448,9 +448,13 @@
   "Username": "用户名",
   "Password": "密码",
   "Backup": "备份",
+  "Local Backup": "本地备份",
+  "WebDAV Backup": "WebDAV 备份",
+  "Select Backup Target": "选择备份目标",
   "Filename": "文件名称",
   "Actions": "操作",
   "Restore": "恢复",
+  "Export": "导出",
   "No Backups": "暂无备份",
   "WebDAV URL Required": "WebDAV 服务器地址不能为空",
   "Invalid WebDAV URL": "无效的 WebDAV 服务器地址格式",
@@ -461,7 +465,13 @@
   "WebDAV Config Save Failed": "保存 WebDAV 配置失败: {{error}}",
   "Backup Created": "备份创建成功",
   "Backup Failed": "备份失败: {{error}}",
+  "Local Backup Created": "本地备份创建成功",
+  "Local Backup Failed": "本地备份失败",
+  "Local Backup Exported": "本地备份导出成功",
+  "Local Backup Export Failed": "本地备份导出失败",
+  "Local Backup Info": "在应用数据目录中创建本地备份，您可以通过下方列表进行恢复或删除。",
   "Delete Backup": "删除备份",
+  "Export Backup": "导出备份",
   "Restore Backup": "恢复备份",
   "Backup Time": "备份时间",
   "Confirm to delete this backup file?": "确认删除此备份文件吗？",