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/mermaid.md

@@ -0,0 +1,99 @@
+# Mermaid quick start
+
+Mermaid diagrams stream progressively in `markstream-vue`: as soon as the syntax becomes valid the chart renders, then refines as more tokens arrive. This page covers setup, a streaming example, and common fixes.
+
+## 1. Install & import
+
+```bash
+pnpm add mermaid
+```
+
+No extra Mermaid CSS import is required. Keep `markstream-vue/index.css` after your reset and inside `@layer components` when using Tailwind/UnoCSS so utility layers do not override the renderer styles.
+
+```css
+@import 'modern-css-reset';
+
+@layer components {
+  @import 'markstream-vue/index.css';
+}
+```
+
+## 2. Streaming example
+
+Mermaid renders as soon as the snippet is syntactically valid. The snippet below shows a gradual update (ideal for AI responses or long-running tasks):
+
+```vue twoslash
+<script setup lang="ts">
+import MarkdownRender from 'markstream-vue'
+import { ref } from 'vue'
+
+const content = ref('')
+const steps = [
+  '```mermaid\n',
+  'graph TD\n',
+  'A[Start]-->B{Is valid?}\n',
+  'B -- Yes --> C[Render]\n',
+  'B -- No  --> D[Wait]\n',
+  '```\n',
+]
+
+let i = 0
+const id = setInterval(() => {
+  content.value += steps[i] || ''
+  i++
+  if (i >= steps.length)
+    clearInterval(id)
+}, 120)
+</script>
+
+<template>
+  <MarkdownRender :content="content" />
+  <!-- Diagram progressively appears as content streams in -->
+</template>
+```
+
+Quick try — paste this Markdown into a page or component:
+
+```md
+\`\`\`mermaid
+graph LR
+A[Start]-->B
+B-->C[End]
+\`\`\`
+```
+
+![Mermaid demo](/screenshots/mermaid-demo.svg)
+
+## 3. Advanced component: `MermaidBlockNode`
+
+Need header controls, export buttons, or a pseudo-fullscreen modal? Use [`MermaidBlockNode`](/guide/mermaid-block-node) or override the default renderer via [setCustomComponents](/guide/mermaid-block-node-override). A runnable playground demo lives at `/mermaid-export-demo`.
+If diagrams come from untrusted users/LLMs, pass `:is-strict="true"` to enable Mermaid's strict mode and SVG sanitization so injected HTML/event handlers are stripped before render.
+
+## 4. Troubleshooting checklist
+
+1. **Peer not installed** — run `pnpm add mermaid`. Without it the renderer falls back to showing source text.
+2. **Async errors** — check the browser console for Mermaid logs. Versions prior to 11 are unsupported; upgrade to ≥ 11.
+3. **SSR guard** — Mermaid needs the DOM. Wrap the component in `<ClientOnly>` for Nuxt or check `typeof window !== 'undefined'` before mounting in SSR contexts.
+4. **Heavy graphs** — consider pre-rendering server-side (mermaid CLI) or caching SVG output; the component exposes `svgString` when using `MermaidBlockNode` export events.
+
+Still stuck? Reproduce the issue in the playground (`pnpm play`) with a minimal Markdown sample and link it when opening a bug report.
+
+## CDN usage (no bundler)
+
+If you load Mermaid via CDN and want progressive off-main-thread parsing, inject a CDN-backed worker:
+
+```ts twoslash
+import { createMermaidWorkerFromCDN, enableMermaid, setMermaidLoader, setMermaidWorker } from 'markstream-vue'
+
+// use the CDN global (UMD) on the main thread
+setMermaidLoader(() => (window as any).mermaid)
+enableMermaid(() => (window as any).mermaid)
+
+// optional: worker used for parse/prefix checks during streaming
+const { worker } = createMermaidWorkerFromCDN({
+  mode: 'module',
+  mermaidUrl: 'https://cdn.jsdelivr.net/npm/mermaid@11/dist/mermaid.esm.min.mjs',
+})
+if (worker)
+  setMermaidWorker(worker)
+```