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/package.json

@@ -0,0 +1,41 @@
+{
+  "name": "playground",
+  "type": "module",
+  "private": true,
+  "scripts": {
+    "build": "vite build",
+    "dev": "vite --port 3333 --open",
+    "typecheck": "vue-tsc --noEmit",
+    "preview": "vite preview",
+    "test": "vitest"
+  },
+  "dependencies": {
+    "@iconify-json/carbon": "^1.2.20",
+    "@iconify/vue": "^5.0.0",
+    "@tailwindcss/typography": "^0.5.19",
+    "@terrastruct/d2": ">=0.1.33",
+    "@vueuse/core": "^13.9.0",
+    "drauu": "^1.0.0",
+    "katex": "^0.16.44",
+    "markstream-vue": "workspace:*",
+    "stream-markdown": "latest",
+    "stream-markdown-parser": "workspace:*",
+    "stream-monaco": "latest",
+    "vite": "^7.3.1",
+    "vue": "^3.5.31",
+    "vue-i18n": "^11.3.0",
+    "vue-router": "^4.6.4"
+  },
+  "devDependencies": {
+    "@types/node": "^20.19.37",
+    "@unocss/reset": "^0.61.9",
+    "@vue/test-utils": "^2.4.6",
+    "eslint": "^9.39.4",
+    "jsdom": "^24.1.3",
+    "monaco-editor": "^0.52.2",
+    "pinia": "^3.0.4",
+    "unplugin-auto-import": "^0.18.6",
+    "unplugin-vue-components": "^0.27.5",
+    "vite-plugin-monaco-editor-esm": "^2.0.2"
+  }
+}