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/stream-monaco/examples/streaming-demo/src/router.ts

@@ -0,0 +1,15 @@
+import { createRouter, createWebHistory } from 'vue-router'
+import DiffDemo from './DiffDemo.vue'
+import DiffUXDemo from './DiffUXDemo.vue'
+import StreamingDemo from './StreamingDemo.vue'
+
+const routes = [
+  { path: '/', name: 'stream', component: StreamingDemo },
+  { path: '/diff', name: 'diff', component: DiffDemo },
+  { path: '/diff-ux', name: 'diff-ux', component: DiffUXDemo },
+]
+
+export const router = createRouter({
+  history: createWebHistory(),
+  routes,
+})