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/test/probes/parse-probe-write.js

@@ -0,0 +1,33 @@
+const fs = require('node:fs')
+const { parseMarkdownToStructure, getMarkdown } = require('stream-markdown-parser')
+
+const md = getMarkdown('midstates')
+
+const probes = [
+  '#x',
+  '`x',
+  '[x](http://a',
+  '```mermaid\nflowchart TD\nA-->B',
+  '- [ ] x\n',
+  'Title\n===',
+  '``x',
+  '~~**x',
+  '[:smile:x](http://a',
+  'a | b\n---|---',
+  '```js { foo:1 }',
+  '<div',
+  '::: tip\ncontent\n:::',
+]
+
+const out = []
+for (const p of probes) {
+  try {
+    const nodes = parseMarkdownToStructure(p, md)
+    out.push({ input: p, nodes })
+  }
+  catch (e) {
+    out.push({ input: p, error: String((e && e.stack) || e) })
+  }
+}
+fs.writeFileSync('test/probes/parse-output.json', JSON.stringify(out, null, 2), 'utf8')
+console.log('WROTE test/probes/parse-output.json')

desktop/libs/markstream-vue/test/probes/parse-probe.js

@@ -0,0 +1,26 @@
+const { parseMarkdownToStructure, getMarkdown } = require('stream-markdown-parser')
+
+const md = getMarkdown('midstates')
+
+const probes = [
+  '#x',
+  '`x',
+  '[x](http://a',
+  '```mermaid\nflowchart TD\nA-->B',
+  '- [ ] x\n',
+  'Title\n===',
+  '``x',
+  '~~**x',
+  '[:smile:x](http://a',
+]
+
+for (const p of probes) {
+  try {
+    const nodes = parseMarkdownToStructure(p, md)
+    console.log('--- INPUT:', JSON.stringify(p))
+    console.log(JSON.stringify(nodes, null, 2))
+  }
+  catch (e) {
+    console.error('ERROR for input', p, (e && e.stack) || e)
+  }
+}