feat(i18n): add multi-language support (ja/ko/vi/ru/zh-TW) with system auto-detection

- Extend AppLanguage to 7 locales: zh-CN, zh-TW, en, ja, ko, vi, ru
- Auto-detect system language via navigator.languages; fallback to English
- Add BCP47 locale mapping for date formatting and sorting
- Create 50 translation JSON files (5 languages × 10 namespaces, 1137 keys each)
- Update language selector with native language names
- Extend locale key parity test to cover all 7 languages (70 assertions)
- Add VNC/RDP desktop, serial terminal, AI agent, port forwarding, and SFTP features
- Add credential encryption, host metrics, session backup crypto, and zmodem bridge
- Update Rust backend: desktop services, host metrics, SSH/SFTP enhancements

src/i18n/locales/zh-CN/desktop.json

@@ -0,0 +1,44 @@
+{
+  "connect": {
+    "rdpTitle": "连接 RDP",
+    "vncTitle": "连接 VNC",
+    "rdpDesc": "Windows 远程桌面 · 原生 IronRDP 引擎",
+    "vncDesc": "VNC / RFB 远程桌面 · 原生引擎",
+    "confirm": "连接",
+    "host": "主机",
+    "hostPlaceholderRdp": "windows.example.com",
+    "hostPlaceholderVnc": "192.168.1.10",
+    "port": "端口",
+    "username": "用户名",
+    "domain": "域名（可选）",
+    "password": "密码",
+    "passwordOptional": "密码（可选）",
+    "width": "宽度",
+    "height": "高度",
+    "rdpFootnote": "原生 IronRDP：TCP → X.224 → TLS → CredSSP/NLA → MCS；握手超时 45s。证书校验当前为开发期宽松模式。",
+    "vncFootnote": "原生 vnc-rs RFB：支持 Tight JPEG 帧解码；剪贴板按 UTF-8 发送（极旧服务端可能乱码）。",
+    "errorHostRequired": "请输入主机地址",
+    "errorUsernameRequired": "请输入用户名"
+  },
+  "toolbar": {
+    "pasteClipboard": "粘贴本机剪贴板到远端",
+    "pasteAria": "粘贴到远端",
+    "shareDrive": "把本地文件复制到共享盘（本机「下载」= 远端「Downloads on OpsXShell」）",
+    "shareDriveAria": "放入共享盘",
+    "openShareDir": "在本机打开共享目录（下载文件夹）",
+    "openShareDirAria": "打开共享目录",
+    "disconnect": "断开连接",
+    "disconnectAria": "断开连接"
+  },
+  "status": {
+    "connecting": "正在连接…",
+    "connected": "已连接",
+    "disconnected": "已断开",
+    "connectFailed": "连接失败",
+    "clipboardSynced": "已同步远端剪贴板",
+    "savedToDownloads": "已保存到本机下载文件夹：{{name}}",
+    "pastedToRemote": "已粘贴到远端",
+    "fileTooLarge": "单文件上限 50MB",
+    "fileShared": "已放入共享盘「下载」：{{name}}（远端此电脑可见）"
+  }
+}