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/infographic.md

@@ -0,0 +1,35 @@
+# AntV Infographic
+
+`markstream-vue` supports rendering [AntV Infographic](https://infographic.antv.vision/) charts.
+
+## 1. Installation
+
+This feature depends on the `@antv/infographic` library.
+
+```bash
+npm install @antv/infographic
+```
+
+## 2. Example
+
+Use the `infographic` code block in Markdown to render charts:
+
+````md
+```infographic
+infographic list-row-simple-horizontal-arrow
+data
+  items
+    - label Step 1
+      desc Start
+    - label Step 2
+      desc Processing
+    - label Step 3
+      desc Complete
+```
+````
+
+![Infographic demo](/screenshots/infographic-demo.png)
+
+## 3. Resources
+
+- [AntV Infographic Official Website](https://infographic.antv.vision/) - Explore more chart templates and syntax details.