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/sftp/TransferPanel.tsx

@@ -4,6 +4,7 @@
  * 显示文件上传/下载的传输队列
  */
 
+import { useTranslation } from 'react-i18next'
 import { ChevronDown, ChevronUp } from 'lucide-react'
 import { TransferItem } from './TransferItem'
 import type { TransferTask } from '../../../shared/types/sftp.types'
@@ -17,36 +18,35 @@ interface TransferPanelProps {
 }
 
 export function TransferPanel({ tasks, isOpen, onToggle, onCancel, onRemove }: TransferPanelProps) {
+  const { t } = useTranslation('sftp')
   const activeCount = tasks.filter(t => t.status === 'pending' || t.status === 'transferring').length
   const completedCount = tasks.filter(t => t.status === 'completed').length
 
   return (
     <div className="bg-dark-800 border-t border-dark-700/30">
-      {/* Header */}
       <button
         onClick={onToggle}
         className="w-full flex items-center justify-between px-4 py-2 hover:bg-dark-700 transition-colors"
       >
         <div className="flex items-center gap-2">
-          <span className="text-sm font-medium">传输队列</span>
+          <span className="text-sm font-medium">{t('transfer.queue')}</span>
           {activeCount > 0 && (
             <span className="px-2 py-0.5 bg-accent-blue/20 text-accent-blue text-xs rounded-full">
-              {activeCount} 进行中
+              {t('transfer.active', { count: activeCount })}
             </span>
           )}
           {completedCount > 0 && (
             <span className="px-2 py-0.5 bg-green-500/20 text-green-400 text-xs rounded-full">
-              {completedCount} 已完成
+              {t('transfer.completed', { count: completedCount })}
             </span>
           )}
         </div>
         <div className="flex items-center gap-2">
-          <span className="text-xs text-txt-muted">{tasks.length} 个任务</span>
+          <span className="text-xs text-txt-muted">{t('transfer.taskCount', { count: tasks.length })}</span>
           {isOpen ? <ChevronDown className="w-4 h-4" /> : <ChevronUp className="w-4 h-4" />}
         </div>
       </button>
 
-      {/* Transfer List */}
       {isOpen && tasks.length > 0 && (
         <div className="max-h-48 overflow-y-auto border-t border-dark-700/30">
           {tasks.map((task) => (
@@ -62,7 +62,7 @@ export function TransferPanel({ tasks, isOpen, onToggle, onCancel, onRemove }: T
 
       {isOpen && tasks.length === 0 && (
         <div className="py-4 text-center text-txt-muted text-sm">
-          暂无传输任务
+          {t('transfer.empty')}
         </div>
       )}
     </div>