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/quick-start.md

@@ -0,0 +1,57 @@
+---
+description: Start rendering Markdown with markstream-vue in the smallest possible Vue example, including the default CSS behavior and next steps.
+---
+
+# Quick Start
+
+A minimal example using the library:
+
+```vue twoslash
+<script setup lang="ts">
+import MarkdownRender from 'markstream-vue'
+
+type MarkdownRenderProps = InstanceType<typeof MarkdownRender>['$props']
+
+const md: MarkdownRenderProps['content'] = `# Hello World\n\nThis is **bold** and this is *italic*.`
+const customId: MarkdownRenderProps['customId'] = 'quick-start'
+const isDark: MarkdownRenderProps['isDark'] = false
+</script>
+
+<template>
+  <MarkdownRender
+    :content="md"
+    :custom-id="customId"
+    :is-dark="isDark"
+  />
+</template>
+```
+
+If you want prop-level hover, start with `MarkdownRenderProps['content']`, `MarkdownRenderProps['customId']`, `MarkdownRenderProps['isDark']`, or the matching template attributes above. Hovering the component name itself is usually less informative in Vue snippets.
+
+Note: the packaged CSS is scoped under an internal `.markstream-vue` container to reduce global style conflicts. The main package entry already imports the default stylesheet; add `import 'markstream-vue/index.css'` only when you want explicit control over CSS order in your app shell.
+
+For dark theme variables, either add `.dark` on an ancestor or pass `:is-dark="true"` to scope dark mode to the renderer.
+
+Optional: wrap with `<client-only>` for Nuxt/SSR.
+
+See `/nuxt-ssr` for Nuxt-specific instructions.
+
+Try this quickly in your app:
+
+```vue twoslash
+<script setup lang="ts">
+import MarkdownRender from 'markstream-vue'
+
+type MarkdownRenderProps = InstanceType<typeof MarkdownRender>['$props']
+
+const md: MarkdownRenderProps['content'] = `# Hello world\n\nTry a simple Mermaid:\n\n\`\`\`mermaid\ngraph LR\nA-->B\n\`\`\`\n\nTry a simple D2:\n\n\`\`\`d2\ndirection: right\nClient -> API: request\nAPI -> DB: query\nDB -> API: rows\nAPI -> Client: response\n\`\`\`\n`
+</script>
+
+<template>
+  <MarkdownRender :content="md" />
+</template>
+```
+
+Install `mermaid` or `@terrastruct/d2` to render those diagrams; without them the renderer falls back to showing source text.
+
+For high-frequency streaming, the highest-throughput setup is usually: parse outside the component and pass `:nodes` into `MarkdownRender`, instead of reparsing the entire `content` string every token. See `/guide/usage` and `/guide/performance`.