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/ensure-next-client-directive.mjs

@@ -0,0 +1,11 @@
+import { readFileSync, writeFileSync } from 'node:fs'
+import path from 'node:path'
+import { fileURLToPath } from 'node:url'
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url))
+const nextEntryPath = path.resolve(__dirname, '../dist/next.js')
+const source = readFileSync(nextEntryPath, 'utf8')
+
+if (!source.startsWith('\'use client\';')) {
+  writeFileSync(nextEntryPath, `'use client';\n${source}`)
+}