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/zh/guide/react-next-ssr.md

@@ -0,0 +1,83 @@
+# React Next SSR
+
+`markstream-react` 现在提供两条明确的 Next.js SSR 入口：
+
+- `markstream-react/next`：Next 官方接入入口。适合 App Router 的 Server Component 和 Pages Router 的 SSR 页面。首包先输出真实服务端 HTML，重节点在 hydration 后再增强。
+- `markstream-react/server`：纯 server 入口。适合完全不进入 client component 边界、只输出稳定 fallback HTML 的路径。
+
+样式只需要在应用壳层引入一次：
+
+```tsx
+// app/layout.tsx 或 pages/_app.tsx
+import 'markstream-react/index.css'
+import 'katex/dist/katex.min.css'
+```
+
+## 在 App Router 中使用 `markstream-react/next`
+
+```tsx
+import MarkdownRender from 'markstream-react/next'
+
+const markdown = `# Hello Next.js
+
+这个路由会先返回真实 SSR HTML。`
+
+export default function Page() {
+  return <MarkdownRender content={markdown} final />
+}
+```
+
+## 使用 `markstream-react/server` 做纯服务端渲染
+
+```tsx
+import MarkdownRender from 'markstream-react/server'
+
+const markdown = `# Server entry
+
+这条路径保持纯服务端渲染。`
+
+export default function Page() {
+  return <MarkdownRender content={markdown} final />
+}
+```
+
+## 自定义组件与自定义标签
+
+如果你在服务端文件里注册 override，优先从 server 入口拿 helper，避免引入 root 入口副作用：
+
+```tsx
+import MarkdownRender, { setCustomComponents } from 'markstream-react/server'
+
+setCustomComponents('next-ssr-demo', {
+  thinking: ({ children }: any) => <aside data-ssr-status="thinking-tag">{children}</aside>,
+})
+```
+
+然后配合 `customId="next-ssr-demo"` 和 `customHtmlTags={['thinking']}` 渲染。
+
+当前 SSR 验收还会显式检查：
+
+- `customId` 作用域隔离
+- custom node 的 `children` 是否进入首包 HTML
+- `customHtmlTags` 的 attrs 是否保留在首包 HTML
+
+## TypeScript
+
+`markstream-react/next` 和 `markstream-react/server` 都会发布独立声明文件。公共 props 类型可以直接从你实际使用的入口导入：
+
+```tsx
+import type {
+  HtmlPreviewFrameProps,
+  MarkdownCodeBlockNodeProps,
+  NodeRendererProps,
+  TooltipProps,
+} from 'markstream-react/next'
+```
+
+## 当前验证命令
+
+```bash
+pnpm exec vitest run test/markstream-react-next-ssr.test.tsx
+pnpm --filter markstream-react build
+pnpm run test:e2e:next-ssr
+```