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/guide/react-next-ssr.md

@@ -0,0 +1,83 @@
+# React Next SSR
+
+`markstream-react` now exposes two explicit SSR entrypoints for Next.js:
+
+- `markstream-react/next`: the official Next entry. Import it from App Router server components or Pages Router SSR pages when you want real server HTML first and client enhancement after hydration.
+- `markstream-react/server`: a pure server entry. Use it when you want a stable server-only render path with no client component boundary.
+
+Import styles once from your app shell:
+
+```tsx
+// app/layout.tsx or pages/_app.tsx
+import 'markstream-react/index.css'
+import 'katex/dist/katex.min.css'
+```
+
+## App Router with `markstream-react/next`
+
+```tsx
+import MarkdownRender from 'markstream-react/next'
+
+const markdown = `# Hello Next.js
+
+This route ships real SSR HTML first.`
+
+export default function Page() {
+  return <MarkdownRender content={markdown} final />
+}
+```
+
+## Pure Server Rendering with `markstream-react/server`
+
+```tsx
+import MarkdownRender from 'markstream-react/server'
+
+const markdown = `# Server entry
+
+This path stays fully server-rendered.`
+
+export default function Page() {
+  return <MarkdownRender content={markdown} final />
+}
+```
+
+## Custom Components and Custom Tags
+
+If you register overrides from a server file, prefer the server helpers so you avoid importing the root package side effects:
+
+```tsx
+import MarkdownRender, { setCustomComponents } from 'markstream-react/server'
+
+setCustomComponents('next-ssr-demo', {
+  thinking: ({ children }: any) => <aside data-ssr-status="thinking-tag">{children}</aside>,
+})
+```
+
+Then render with `customId="next-ssr-demo"` and `customHtmlTags={['thinking']}`.
+
+Current SSR acceptance also covers:
+
+- `customId` scoping isolation
+- custom node children rendered into the initial HTML
+- `customHtmlTags` attributes preserved in the initial HTML
+
+## TypeScript
+
+`markstream-react/next` and `markstream-react/server` both publish standalone declaration files. You can import shared prop types directly from the entrypoint you use:
+
+```tsx
+import type {
+  HtmlPreviewFrameProps,
+  MarkdownCodeBlockNodeProps,
+  NodeRendererProps,
+  TooltipProps,
+} from 'markstream-react/next'
+```
+
+## Current Verification Commands
+
+```bash
+pnpm exec vitest run test/markstream-react-next-ssr.test.tsx
+pnpm --filter markstream-react build
+pnpm run test:e2e:next-ssr
+```