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/AiEntryPoints.test.tsx

@@ -27,7 +27,8 @@ describe('AI entry points', () => {
     const entry = screen.getByTestId('settings-tab-ai')
     expect(entry).toBeVisible()
     expect(entry).toHaveTextContent('大模型')
-    expect(entry).toHaveTextContent('Provider、模型与测试')
+    expect(entry).toHaveTextContent('Provider')
+    expect(entry).not.toHaveTextContent('模型与测试')
 
     fireEvent.click(entry)
     expect(screen.getByRole('heading', { name: '大模型' })).toBeVisible()