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/App.acceptance.test.tsx

@@ -1,7 +1,10 @@
 import { fireEvent, render, screen, waitFor } from '@testing-library/react'
+import userEvent from '@testing-library/user-event'
 import { afterEach, describe, expect, it, vi } from 'vitest'
 import App from '../../src/app/App'
 import { useSessionStore } from '../../src/stores/sessionStore'
+import { decodeBase64ToText } from '../../src/utils/textBase64'
+import { decryptSessionBackup } from '../../src/utils/sessionBackupCrypto'
 import { mockDesktopApi } from '../setup'
 import { unlockProForTests } from '../helpers/entitlement'
 
@@ -16,8 +19,9 @@ describe('App foundation acceptance', () => {
     expect(await screen.findByRole('heading', { name: 'OpsXShell' })).toBeVisible()
     expect(mockDesktopApi.onMenuOpenSettings).toHaveBeenCalled()
 
-    const title = screen.getByText('OpsXShell', { selector: 'span' })
-    expect(title.closest('header')).toHaveAttribute('data-tauri-drag-region')
+    const titleBar = document.querySelector('header[data-tauri-drag-region]')
+    expect(titleBar).toBeTruthy()
+    expect(titleBar).toHaveAttribute('data-tauri-drag-region')
   })
 
   it('renders the shell while the native bridge is unavailable', async () => {
@@ -50,8 +54,8 @@ describe('App foundation acceptance', () => {
     window.opsxApi = mockDesktopApi
     render(<App />)
 
-    const title = await screen.findByText('OpsXShell', { selector: 'span' })
-    const titleBar = title.closest('header')
+    await screen.findByRole('heading', { name: 'OpsXShell' })
+    const titleBar = document.querySelector('header[data-tauri-drag-region]')
     expect(titleBar).toHaveAttribute('data-tauri-drag-region')
     expect(titleBar).not.toHaveClass('titlebar-drag')
 
@@ -59,7 +63,8 @@ describe('App foundation acceptance', () => {
     expect(mockDesktopApi.toggleMaximize).not.toHaveBeenCalled()
   })
 
-  it('writes exported sessions to the selected JSON file', async () => {
+  it('writes encrypted exported sessions to the selected backup file', async () => {
+    const user = userEvent.setup()
     vi.clearAllMocks()
     unlockProForTests()
     vi.mocked(mockDesktopApi.licenseGet).mockResolvedValue({
@@ -83,17 +88,39 @@ describe('App foundation acceptance', () => {
     })
     vi.mocked(mockDesktopApi.showSaveDialog).mockResolvedValueOnce({
       canceled: false,
-      filePath: '/tmp/opsxshell-sessions.json',
+      filePath: '/tmp/opsxshell-sessions.bak',
     })
     render(<App />)
 
     await waitFor(() => expect(mockDesktopApi.onMenuExportSessions).toHaveBeenCalled())
     const callback = vi.mocked(mockDesktopApi.onMenuExportSessions).mock.calls[0][0]
-    await callback()
+    const exportPromise = callback()
 
-    expect(mockDesktopApi.writeFile).toHaveBeenCalledWith(
-      '/tmp/opsxshell-sessions.json',
-      expect.stringContaining('"prod.example.com"')
+    const passwordInput = await screen.findByPlaceholderText('输入备份密码')
+    await user.type(passwordInput, 'backup-secret')
+    await user.click(screen.getByRole('button', { name: '确认' }))
+
+    const confirmInput = await screen.findByPlaceholderText('再次输入备份密码')
+    await user.type(confirmInput, 'backup-secret')
+    await user.click(screen.getByRole('button', { name: '确认' }))
+
+    await exportPromise
+
+    expect(mockDesktopApi.showSaveDialog).toHaveBeenCalledWith(
+      expect.objectContaining({
+        defaultPath: 'opsxshell-sessions.bak',
+      })
     )
+    expect(mockDesktopApi.writeFile).toHaveBeenCalledWith(
+      '/tmp/opsxshell-sessions.bak',
+      expect.any(String)
+    )
+    const [, encoded] = vi.mocked(mockDesktopApi.writeFile).mock.calls[0]
+    const decoded = decodeBase64ToText(String(encoded))
+    expect(decoded).toContain('"format": "opsxshell-backup"')
+    expect(decoded).not.toContain('prod.example.com')
+    const envelope = JSON.parse(decoded)
+    const plaintext = await decryptSessionBackup(envelope, 'backup-secret')
+    expect(plaintext).toContain('"prod.example.com"')
   })
 })