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/docs/guide/contributing.md

@@ -0,0 +1,40 @@
+# Contributing
+
+Thanks for wanting to contribute!
+
+Development commands to know:
+
+- `pnpm dev` — start the library playground
+- `pnpm play` — start the playground (same as dev)
+- `pnpm build` — build the library
+- `pnpm build:analyze` — build with bundle visualizer reports
+- `pnpm size:check` — enforce package size budgets
+- `pnpm test` — run unit tests
+- `pnpm docs:dev` — start the VitePress docs server
+
+Size budget env overrides (optional):
+
+- `MAX_DIST_BYTES`
+- `MAX_JS_CHUNK_BYTES`
+- `MAX_PACK_TGZ_BYTES`
+- `MAX_PACK_UNPACKED_BYTES`
+
+How to add a docs page:
+
+1. Add a markdown file under `docs/` or `docs/guide`.
+2. Update `docs/.vitepress/config.ts` sidebar if needed.
+3. Run `pnpm docs:dev` to preview the page locally and ensure everything builds.
+4. Open a PR with your changes.
+
+Guidelines:
+
+- Keep docs concise and example-driven
+- If adding code snippets to docs, verify they run in `playground` or tests
+- Add tests for any new features in `test/` and update `README` / docs accordingly
+
+Quick try — run the docs site locally and add a simple page to verify the flow:
+
+```bash
+pnpm docs:dev
+# open http://localhost:5173, add docs/guide/new-page.md and confirm build
+```