feat(desktop): embed BoosAPI Desktop client as a subproject

Vendor the rebranded BoosAPI Desktop client (Tauri + Vue) into metapi as
a monorepo subdirectory under desktop/. Source only — node_modules,
dist, Cargo target and the upstream .git history are excluded.

desktop/ keeps its own independent Cargo workspace (desktop/src-tauri
with crates/*); it is not part of the backend boosapi crate, so a
`cargo check` at the metapi root still compiles only the backend. Build
the desktop app from desktop/src-tauri per desktop/README.md.

Note: app icons are still placeholder assets pending the final BoosAPI
logo. The updater signing keys live outside the repo and are not
included.

desktop/src/__tests__/App.d2.test.tsx

@@ -0,0 +1,188 @@
+import { render, waitFor } from '@testing-library/react';
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+
+const enableD2 = vi.fn();
+const preloadChatRenderers = vi.fn();
+const setDefaultI18nMap = vi.fn();
+
+const settingsState = {
+  settings: {
+    theme_mode: 'dark',
+    primary_color: '#17A93D',
+    font_size: 14,
+    font_weight: 400,
+    font_family: '',
+    code_font_family: '',
+    chat_font_size: 16,
+    chat_line_height: 1.8,
+    chat_font_family: 'Inter',
+    chat_font_weight: 500,
+    border_radius: 8,
+    language: 'zh-CN',
+    always_on_top: false,
+    close_to_tray: true,
+    auto_start: false,
+    global_shortcuts_enabled: false,
+    shortcut_registration_logs_enabled: false,
+    shortcut_trigger_toast_enabled: false,
+    global_shortcut: '',
+  },
+  fetchSettings: vi.fn().mockResolvedValue(undefined),
+  setGlobalShortcutStatus: vi.fn(),
+};
+
+const uiState = {
+  activePage: 'chat',
+  enterSettings: vi.fn(),
+  setSettingsSection: vi.fn(),
+  setSelectedProviderId: vi.fn(),
+};
+
+const providerState = {
+  importProviderFromDeepLink: vi.fn(),
+  fetchProviders: vi.fn(),
+};
+
+const conversationState = {
+  startStreamListening: vi.fn(),
+  stopStreamListening: vi.fn(),
+};
+
+vi.mock('antd', () => ({
+  ConfigProvider: ({ children }: { children: React.ReactNode }) => <div>{children}</div>,
+  App: Object.assign(
+    ({ children }: { children: React.ReactNode }) => <div>{children}</div>,
+    {
+      useApp: () => ({
+        modal: {},
+        message: {},
+      }),
+    },
+  ),
+  Layout: Object.assign(
+    ({ children }: { children: React.ReactNode }) => <div>{children}</div>,
+    {
+      Sider: ({ children }: { children: React.ReactNode }) => <div>{children}</div>,
+      Content: ({ children }: { children: React.ReactNode }) => <div>{children}</div>,
+    },
+  ),
+  theme: {
+    useToken: () => ({
+      token: {
+        colorBorderSecondary: '#444',
+        colorBgContainer: '#111',
+        colorBgElevated: '#1a1a1a',
+        colorText: '#f5f5f5',
+        colorTextSecondary: '#999',
+        colorPrimary: '#1677ff',
+      },
+    }),
+  },
+}));
+
+vi.mock('antd/locale/zh_CN', () => ({
+  default: {},
+}));
+
+vi.mock('react-i18next', () => ({
+  initReactI18next: {
+    type: '3rdParty',
+    init: () => {},
+  },
+  useTranslation: () => ({
+    i18n: {
+      language: 'zh-CN',
+      getFixedT: () => (_key: string) => _key,
+      changeLanguage: vi.fn(),
+    },
+  }),
+}));
+
+vi.mock('@/components/layout/Sidebar', () => ({
+  Sidebar: () => <div>sidebar</div>,
+}));
+
+vi.mock('@/components/layout/TitleBar', () => ({
+  TitleBar: () => <div>titlebar</div>,
+}));
+
+vi.mock('@/components/layout/ContentArea', () => ({
+  ContentArea: () => <div>content</div>,
+}));
+
+vi.mock('@/components/layout/CommandPalette', () => ({
+  default: () => null,
+}));
+
+vi.mock('@/hooks/useCommandPalette', () => ({
+  useCommandPalette: () => ({
+    open: false,
+    setOpen: vi.fn(),
+  }),
+}));
+
+vi.mock('@/stores', () => ({
+  useUIStore: (selector: (state: typeof uiState) => unknown) => selector(uiState),
+  useProviderStore: (selector: (state: typeof providerState) => unknown) => selector(providerState),
+  useConversationStore: (selector: (state: typeof conversationState) => unknown) => selector(conversationState),
+  useSettingsStore: Object.assign(
+    (selector: (state: typeof settingsState) => unknown) => selector(settingsState),
+    {
+      getState: () => settingsState,
+    },
+  ),
+}));
+
+vi.mock('@/hooks/useKeyboardShortcuts', () => ({
+  useKeyboardShortcuts: vi.fn(),
+}));
+
+vi.mock('@/hooks/useResolvedDarkMode', () => ({
+  useResolvedDarkMode: () => true,
+}));
+
+vi.mock('@/theme/shadcnTheme', () => ({
+  useShadcnTheme: () => ({}),
+}));
+
+vi.mock('@/lib/invoke', () => ({
+  isTauri: () => false,
+}));
+
+vi.mock('@/lib/preloadChatRenderers', () => ({
+  preloadChatRenderers,
+}));
+
+vi.mock('markstream-react', () => ({
+  enableD2,
+  setDefaultI18nMap,
+}));
+
+describe('AppRoot D2 setup', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    document.documentElement.style.cssText = '';
+  });
+
+  it('enables the markstream D2 loader during startup', async () => {
+    const { default: AppRoot } = await import('../App');
+
+    render(<AppRoot />);
+
+    expect(enableD2).toHaveBeenCalledTimes(1);
+    expect(preloadChatRenderers).toHaveBeenCalledTimes(1);
+  });
+
+  it('syncs chat typography settings to CSS variables', async () => {
+    const { default: AppRoot } = await import('../App');
+
+    render(<AppRoot />);
+
+    await waitFor(() => {
+      expect(document.documentElement.style.getPropertyValue('--chat-font-size')).toBe('16px');
+      expect(document.documentElement.style.getPropertyValue('--chat-line-height')).toBe('1.8');
+      expect(document.documentElement.style.getPropertyValue('--chat-font-family')).toBe('Inter');
+      expect(document.documentElement.style.getPropertyValue('--chat-font-weight')).toBe('500');
+    });
+  });
+});