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/examples.md

@@ -0,0 +1,45 @@
+# 示例
+
+简明示例；交互演示请查看 `playground`。以下为中文示例并附带注释：
+
+## 流式 Markdown
+
+这是将字符逐步添加到 `content` 中并让 `MarkdownRender` 渲染的最小示例：
+
+```vue
+<script setup lang="ts">
+import MarkdownRender from 'markstream-vue'
+import { ref } from 'vue'
+
+const content = ref('')
+const fullContent = `# Streaming Content\n\nThis text appears progressively...`
+let i = 0
+const interval = setInterval(() => {
+  if (i < fullContent.length) {
+    content.value += fullContent[i]
+    i++
+  }
+  else {
+    clearInterval(interval)
+  }
+}, 50)
+</script>
+
+<template>
+  <MarkdownRender :content="content" />
+</template>
+```
+
+## 使用 `nodes`
+
+如果你想跳过字符串解析阶段，可直接传入解析后的节点：
+
+```ts
+import { getMarkdown, parseMarkdownToStructure } from 'stream-markdown-parser'
+
+const md = getMarkdown()
+const nodes = parseMarkdownToStructure('# Hello', md)
+// 在 Vue 中传入 nodes 而不是 content
+```
+
+更多示例请查看 `/zh/guide/examples` 或 demo playground 页面。