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-react19/vite.config.js

@@ -0,0 +1,40 @@
+import path from 'node:path'
+import react from '@vitejs/plugin-react-swc'
+import { defineConfig } from 'vite'
+import monacoEditorPlugin from 'vite-plugin-monaco-editor-esm'
+
+export default defineConfig(({ mode }) => ({
+  base: './',
+  server: {
+    port: 4174,
+  },
+  worker: {
+    format: 'es',
+  },
+  optimizeDeps: {
+    exclude: ['stream-monaco'],
+  },
+  // Only use alias in dev mode - for production build, use the built package
+  resolve: mode === 'development'
+    ? {
+        alias: {
+          'markstream-react': path.resolve(__dirname, '../packages/markstream-react/src'),
+        },
+      }
+    : undefined,
+  plugins: [
+    react(),
+    monacoEditorPlugin({
+      languageWorkers: [
+        'editorWorkerService',
+        'typescript',
+        'css',
+        'html',
+        'json',
+      ],
+      customDistPath(_root, buildOutDir) {
+        return path.resolve(buildOutDir, 'monacoeditorwork')
+      },
+    }),
+  ],
+}))