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/components/common/Toast.tsx

@@ -6,6 +6,7 @@
  */
 
 import { useEffect, useState, useCallback } from 'react'
+import { useTranslation } from 'react-i18next'
 import { CheckCircle, XCircle, AlertTriangle, Info, X } from 'lucide-react'
 import { useToastStore, type ToastItem, type ToastType } from '../../stores/toastStore'
 
@@ -56,6 +57,7 @@ interface ToastItemProps {
  * 支持自动消失和手动关闭，带入场/退场动画
  */
 function ToastItemView({ toast, onClose }: ToastItemProps) {
+  const { t } = useTranslation('common')
   const [visible, setVisible] = useState(false)
   const Icon = iconMap[toast.type]
   const colors = colorMap[toast.type]
@@ -107,7 +109,7 @@ function ToastItemView({ toast, onClose }: ToastItemProps) {
       <button
         onClick={handleClose}
         className="p-0.5 rounded hover:bg-white/10 transition-colors shrink-0"
-        aria-label="关闭通知"
+        aria-label={t('toast.closeAria')}
       >
         <X className="w-4 h-4 text-txt-muted hover:text-content-primary" />
       </button>