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/playground-nuxt/package.json

@@ -0,0 +1,26 @@
+{
+  "name": "playground-nuxt",
+  "type": "module",
+  "private": true,
+  "scripts": {
+    "dev": "nuxt dev",
+    "build": "nuxt build",
+    "preview": "nuxt preview",
+    "typecheck": "nuxt typecheck"
+  },
+  "dependencies": {
+    "@iconify-json/carbon": "^1.2.20",
+    "@iconify/vue": "^5.0.0",
+    "@nuxtjs/tailwindcss": "^6.14.0",
+    "@unocss/reset": "^0.61.9",
+    "@vueuse/core": "^13.9.0",
+    "katex": "^0.16.44",
+    "markstream-vue": "workspace:*",
+    "mermaid": "^11.13.0",
+    "monaco-editor": "^0.52.2",
+    "nuxt": "^4.4.2",
+    "stream-markdown": "latest",
+    "stream-monaco": "latest",
+    "vue-i18n": "^11.3.0"
+  }
+}