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/packages/markstream-react/scripts/rollup.dts.config.mjs

@@ -0,0 +1,50 @@
+import fs from 'node:fs'
+import path from 'node:path'
+import dts from 'rollup-plugin-dts'
+
+const entryNames = ['index', 'next', 'server']
+
+function resolveInputPath(entryName) {
+  const preferred = [
+    `./dist/types/${entryName}.d.ts`,
+    entryName === 'index' ? './dist/types/exports.d.ts' : null,
+    `./dist/${entryName}.d.ts`,
+  ].filter(Boolean)
+
+  return preferred.find(p => fs.existsSync(path.resolve(p))) ?? null
+}
+
+const configs = entryNames.map((entryName) => {
+  const inputPath = resolveInputPath(entryName)
+  if (!inputPath) {
+    throw new Error(
+      `No declaration entry found for "${entryName}". Run \`pnpm run build\` before running \`build:dts\`.`,
+    )
+  }
+
+  return {
+    input: inputPath,
+    plugins: [
+      dts({
+        respectExternal: false,
+      }),
+    ],
+    external: [
+      /^node:.*$/,
+      /^react(?:\/.*)?$/,
+      /^react-dom(?:\/.*)?$/,
+      /^(?:katex|mermaid|stream-monaco|stream-markdown)(?:\/.*)?$/,
+      /^stream-markdown-parser(?:\/.*)?$/,
+      /^@antv\/infographic(?:\/.*)?$/,
+      /^@floating-ui\/dom(?:\/.*)?$/,
+    ],
+    output: [
+      {
+        file: `dist/${entryName}.d.ts`,
+        format: 'es',
+      },
+    ],
+  }
+})
+
+export default configs