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/HostKeyDialog.test.tsx

@@ -0,0 +1,52 @@
+/**
+ * HostKeyDialog — first-connect / changed-key confirmation
+ */
+
+import { render, screen } from '@testing-library/react'
+import userEvent from '@testing-library/user-event'
+import { describe, expect, it, vi } from 'vitest'
+import HostKeyDialog from '../../src/components/terminal/HostKeyDialog'
+
+describe('HostKeyDialog', () => {
+  it('emits accept-always for a new host key', async () => {
+    const user = userEvent.setup()
+    const onDecision = vi.fn()
+    render(
+      <HostKeyDialog
+        open
+        host="ops.example.com"
+        port={22}
+        keyType="ssh-ed25519"
+        fingerprint="AAAA"
+        isChanged={false}
+        onDecision={onDecision}
+      />
+    )
+
+    expect(screen.getByText('确认主机密钥')).toBeVisible()
+    await user.click(screen.getByRole('button', { name: '始终信任' }))
+    expect(onDecision).toHaveBeenCalledWith('accept-always')
+  })
+
+  it('shows previous fingerprint when the key changed', async () => {
+    const user = userEvent.setup()
+    const onDecision = vi.fn()
+    render(
+      <HostKeyDialog
+        open
+        host="ops.example.com"
+        port={2222}
+        keyType="ssh-rsa"
+        fingerprint="NEW"
+        isChanged
+        previousFingerprint="OLD"
+        onDecision={onDecision}
+      />
+    )
+
+    expect(screen.getByText('主机密钥已变更')).toBeVisible()
+    expect(screen.getByText(/SHA256:OLD/)).toBeVisible()
+    await user.click(screen.getByRole('button', { name: '仍要信任并更新' }))
+    expect(onDecision).toHaveBeenCalledWith('accept-always')
+  })
+})