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/Breadcrumb.tsx

@@ -3,6 +3,7 @@
  */
 
 import { ChevronRight, Home } from 'lucide-react'
+import { useTranslation } from 'react-i18next'
 import { splitPathSegments } from '../../utils/localPath'
 
 interface BreadcrumbProps {
@@ -13,6 +14,7 @@ interface BreadcrumbProps {
 }
 
 export function Breadcrumb({ path, isLocal = false, onNavigate, onHome }: BreadcrumbProps) {
+  const { t } = useTranslation('sftp')
   const { root, parts, join } = splitPathSegments(path || (isLocal ? '' : '/'), isLocal)
   const rootLabel = isLocal && root !== '/' ? root.replace(/\\$/, '') || root : '/'
 
@@ -22,7 +24,7 @@ export function Breadcrumb({ path, isLocal = false, onNavigate, onHome }: Breadc
         type="button"
         onClick={onHome}
         className="flex-shrink-0 rounded p-1.5 transition-colors hover:bg-dark-700"
-        title="主目录"
+        title={t('nav.home')}
       >
         <Home className="h-4 w-4 text-txt-muted" />
       </button>