feat: 完善多账号连接诊断与聊天媒体导出

- 新增微信账号发现、环境诊断和分步数据库连接引导
- 支持按账号安全保存数据库密钥及快速切换账号
- 完善 WCDB 历史消息分片读取和分页状态提示
- 支持导出图片、视频和语音，提供原图优先及缩略图回退
- 更新安装指引、兼容版本说明和相关自动化测试

tests/component/database-connection.test.tsx

@@ -14,6 +14,35 @@ function renderPage(
     dbRoot: '',
     showDbKey: false,
     isFetching: false,
+    isConnecting: false,
+    guideStep: 1 as const,
+    environment: {
+      platform: 'win32',
+      osVersion: 'Windows fixture',
+      appVersion: 'v2.1.6',
+      wechatVersion: '4.1.9.57',
+      dataStructureVersion: '微信 4.x（WCDB）',
+      dataDirectoryDetected: true,
+      diagnosticSummary: 'WechatExplorer: v2.1.6',
+      autoDetectSupported: true,
+      wechatRunning: true,
+      accountIdentified: false,
+      dbConnected: false,
+      encryptionAvailable: true
+    },
+    accounts: [
+      {
+        id: 'account-a',
+        accountRoot: 'C:\\fixture\\account-a',
+        directoryName: 'account-a',
+        nickname: '脱敏账号 A',
+        wxid: 'wxid_fixture_a',
+        hasSavedDbKey: true,
+        loginStatus: 'unknown' as const,
+        selectedByInput: true
+      }
+    ],
+    selectedAccountId: 'account-a',
     status: '',
     statusKind: 'normal' as const,
     showMacKeyFaq: false,
@@ -21,8 +50,16 @@ function renderPage(
     onModeChange: vi.fn(),
     onDbKeyChange: vi.fn(),
     onDbRootChange: vi.fn(),
+    onSelectAccount: vi.fn(),
+    onSelectDbRoot: vi.fn(),
     onToggleDbKey: vi.fn(),
     onAutoGetKey: vi.fn(),
+    onRefreshEnvironment: vi.fn(),
+    onGuideNext: vi.fn(),
+    onGuideBack: vi.fn(),
+    onGuideCancel: vi.fn(),
+    onValidateConnection: vi.fn(),
+    onCopyDiagnostics: vi.fn(),
     onManualConnect: vi.fn(),
     onPasteKey: vi.fn(),
     onClearKey: vi.fn(),
@@ -52,4 +89,48 @@ describe('DatabaseConnectionPage', () => {
     expect(onManualConnect).toHaveBeenCalledOnce()
     expect(screen.getByRole('button', { name: '从剪贴板粘贴并安全保存' })).toBeEnabled()
   })
+
+  it('restores directory editing and selection after a failed connection', async () => {
+    const onDbRootChange = vi.fn()
+    const onSelectDbRoot = vi.fn()
+    renderPage({
+      dbKey: 'b'.repeat(64),
+      dbRoot: 'Z:\\missing-wechat-data',
+      status: '微信数据目录不存在，请重新选择目录',
+      statusKind: 'error',
+      onDbRootChange,
+      onSelectDbRoot
+    })
+
+    await userEvent.clear(screen.getByLabelText('微信数据目录'))
+    await userEvent.type(screen.getByLabelText('微信数据目录'), 'C:\\fixture-account')
+    await userEvent.click(screen.getByRole('button', { name: '选择目录' }))
+
+    expect(onDbRootChange).toHaveBeenCalled()
+    expect(onSelectDbRoot).toHaveBeenCalledOnce()
+    expect(screen.getByRole('button', { name: '连接数据库' })).toBeEnabled()
+  })
+
+  it('supports forward, back, cancel and safe diagnostic actions in onboarding', async () => {
+    const onGuideNext = vi.fn()
+    const onCopyDiagnostics = vi.fn()
+    const { rerender, props } = renderPage({
+      mode: 'automatic',
+      guideStep: 1,
+      onGuideNext,
+      onCopyDiagnostics
+    })
+
+    expect(screen.getByText('4.1.9.57')).toBeVisible()
+    expect(screen.getByText('微信 4.x（WCDB）')).toBeVisible()
+    await userEvent.click(screen.getByRole('button', { name: '复制脱敏诊断摘要' }))
+    await userEvent.click(screen.getByRole('button', { name: '检查完成，继续' }))
+    expect(onCopyDiagnostics).toHaveBeenCalledOnce()
+    expect(onGuideNext).toHaveBeenCalledOnce()
+
+    rerender(<DatabaseConnectionPage {...props} mode="automatic" guideStep={2} />)
+    expect(screen.getByRole('button', { name: '我已准备好' })).toBeEnabled()
+    expect(screen.getByRole('button', { name: '返回上一步' })).toBeEnabled()
+    expect(screen.getByRole('button', { name: '取消并重新检查' })).toBeEnabled()
+  })
 })