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/parser.md

@@ -0,0 +1,10 @@
+# 解析器与 API
+
+本项目基于 `markdown-it-ts`，提供了适用于流式渲染的解析器与钩子：
+
+- `getMarkdown()` — 创建并配置 `markdown-it-ts` 实例
+- `parseMarkdownToStructure(content, md)` — 将 Markdown 转换为 Parser 节点树（用于 `MarkdownRender`）
+- 支持 `preTransformTokens` / `postTransformTokens` 等钩子以定制解析行为
+- 支持流式内联 HTML（`html_inline`）无抖动：吞并半截标签并自动补闭合（保留 `loading` 状态）。
+
+（完整示例与 API 请参见英文版 `/guide/parser` 或中文版 `/zh/guide/parser`，或内部 `packages/markdown-parser/README.md`）