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-next15/next.config.mjs

@@ -0,0 +1,26 @@
+import { resolve } from 'node:path'
+import { fileURLToPath } from 'node:url'
+
+const rootDir = fileURLToPath(new URL('.', import.meta.url))
+const reactAliases = {
+  'react': resolve(rootDir, 'node_modules/react'),
+  'react-dom': resolve(rootDir, 'node_modules/react-dom'),
+  'react/jsx-runtime': resolve(rootDir, 'node_modules/react/jsx-runtime.js'),
+  'react/jsx-dev-runtime': resolve(rootDir, 'node_modules/react/jsx-dev-runtime.js'),
+}
+
+/** @type {import('next').NextConfig} */
+const nextConfig = {
+  transpilePackages: ['markstream-react', 'stream-markdown-parser'],
+  webpack(config, { isServer }) {
+    if (!isServer) {
+      config.resolve.alias = {
+        ...config.resolve.alias,
+        ...reactAliases,
+      }
+    }
+    return config
+  },
+}
+
+export default nextConfig