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/katex-cache-analysis.zh-CN.md

@@ -0,0 +1,17 @@
+---
+title: Worker Cache 性能分析（已迁移）
+search: false
+---
+
+# Worker Cache 性能分析已迁移
+
+该文档的中文内容现在位于 `/zh/katex-cache-analysis`。
+
+<script>
+  if (typeof window !== 'undefined')
+    window.location.replace('/zh/katex-cache-analysis')
+</script>
+
+<noscript>
+  页面已迁移，请访问 <a href="/zh/katex-cache-analysis">/zh/katex-cache-analysis</a>。
+</noscript>