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

test/components/SFTPTransfer.acceptance.test.tsx

@@ -118,7 +118,7 @@ describe('SFTP basic transfer acceptance', () => {
     await screen.findByRole('button', { name: '上传' })
     await user.click(screen.getByRole('button', { name: '上传' }))
 
-    expect(await screen.findByText(/Permission denied/)).toBeVisible()
+    expect(await screen.findByText(/权限不足|Permission denied/)).toBeVisible()
   })
 
   it('uploads by dragging a local row onto the remote panel', async () => {