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/libs/markstream-vue/docs/.vitepress/twoslash/markstream-vue.d.ts

@@ -0,0 +1,61 @@
+import type { DefineComponent } from 'vue'
+import type { BaseNode } from 'stream-markdown-parser'
+import type {
+  CodeBlockDiffHunkActionContext,
+  CodeBlockMonacoOptions,
+  CodeBlockMonacoTheme,
+  CodeBlockNodeProps,
+  CustomComponents,
+  D2BlockNodeProps,
+  ImageNodeProps,
+  MermaidBlockEvent,
+  MermaidBlockNodeProps,
+  PreCodeNodeProps,
+} from '../../../src/exports'
+import type { NodeRendererProps } from '../../../src/types/node-renderer-props'
+
+export type {
+  BaseNode,
+  CodeBlockDiffHunkActionContext,
+  CodeBlockMonacoOptions,
+  CodeBlockMonacoTheme,
+  CodeBlockNodeProps,
+  CustomComponents,
+  D2BlockNodeProps,
+  ImageNodeProps,
+  MermaidBlockEvent,
+  MermaidBlockNodeProps,
+  NodeRendererProps,
+  PreCodeNodeProps,
+}
+
+export {
+  CodeBlockNode,
+  D2BlockNode,
+  ImageNode,
+  MarkdownCodeBlockNode,
+  MermaidBlockNode,
+  PreCodeNode,
+  createKaTeXWorkerFromCDN,
+  createMermaidWorkerFromCDN,
+  enableD2,
+  enableKatex,
+  enableMermaid,
+  getMarkdown,
+  getUseMonaco,
+  parseMarkdownToStructure,
+  preloadExtendedLanguageIcons,
+  removeCustomComponents,
+  setCustomComponents,
+  setD2Loader,
+  setDefaultI18nMap,
+  setDefaultMathOptions,
+  setKaTeXWorker,
+  setKatexLoader,
+  setMermaidLoader,
+  setMermaidWorker,
+} from '../../../src/exports'
+
+export declare const MarkdownRender: DefineComponent<NodeRendererProps>
+
+export default MarkdownRender