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/parser.md

@@ -0,0 +1,26 @@
+# Parser & API
+
+markstream-vue builds on top of `markdown-it-ts` and exposes a streaming-friendly parser.
+
+For the full parser API reference, see:
+- [/guide/parser-api](/guide/parser-api)
+- `stream-markdown-parser` README (parser-only package): https://www.npmjs.com/package/stream-markdown-parser
+
+Highlights:
+
+- `getMarkdown()` — create and configure a `markdown-it-ts` instance
+- `parseMarkdownToStructure(content, md)` — turn a Markdown string into parsed nodes used by `MarkdownRender`
+- `setDefaultMathOptions()` — global math options
+- Streaming inline HTML mid-states (`html_inline`) — suppress partial tags and auto-close unclosed inline HTML for flicker-free streaming.
+
+If you only need the parser (no Vue), install and import from `stream-markdown-parser`. Otherwise, `markstream-vue` re-exports the same helpers for convenience.
+
+Try this quickly — parse a small string and render the result in your app:
+
+```ts
+import { getMarkdown, parseMarkdownToStructure } from 'markstream-vue'
+
+const md = getMarkdown()
+const nodes = parseMarkdownToStructure('# Hello\n\nThis is a test', md)
+// Render nodes with <MarkdownRender :nodes="nodes" />
+```