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/utils/sessionBackupCrypto.test.ts

@@ -0,0 +1,31 @@
+import { describe, expect, it } from 'vitest'
+import {
+  decryptSessionBackup,
+  encryptSessionBackup,
+  isEncryptedSessionBackup,
+} from '../../src/utils/sessionBackupCrypto'
+
+describe('sessionBackupCrypto', () => {
+  it('encrypts and decrypts UTF-8 session payload', async () => {
+    const plaintext = JSON.stringify({
+      version: 1,
+      sessions: [{ name: '生产', host: 'ops.example.com', privateKey: '-----BEGIN KEY-----\n密\n' }],
+    })
+    const encrypted = await encryptSessionBackup(plaintext, 's3cret!')
+    const envelope = JSON.parse(encrypted)
+    expect(isEncryptedSessionBackup(envelope)).toBe(true)
+    expect(encrypted).not.toContain('ops.example.com')
+    expect(encrypted).not.toContain('BEGIN KEY')
+
+    const restored = await decryptSessionBackup(envelope, 's3cret!')
+    expect(restored).toBe(plaintext)
+  })
+
+  it('rejects wrong password', async () => {
+    const encrypted = await encryptSessionBackup('{"sessions":[]}', 'right-password')
+    const envelope = JSON.parse(encrypted)
+    await expect(decryptSessionBackup(envelope, 'wrong-password')).rejects.toThrow(
+      'BACKUP_PASSWORD_INVALID'
+    )
+  })
+})