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/scripts/install-skills.mjs

@@ -0,0 +1,27 @@
+import process from 'node:process'
+import {
+  parseInstallArgs,
+  printInstallHelp,
+  printInstallSummary,
+  runSkillsInstall,
+} from '../bin/skills-lib.mjs'
+
+async function main() {
+  const args = parseInstallArgs(process.argv.slice(2), {
+    target: 'agents',
+    mode: 'symlink',
+  })
+
+  if (args.help) {
+    printInstallHelp('node scripts/install-skills.mjs', 'symlink')
+    return
+  }
+
+  const result = await runSkillsInstall(args)
+  printInstallSummary(result)
+}
+
+main().catch((error) => {
+  console.error(error instanceof Error ? error.message : error)
+  process.exit(1)
+})