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/inline-parsers/checkbox-parser.test.ts

@@ -0,0 +1,26 @@
+import { describe, expect, it } from 'vitest'
+import { parseCheckboxInputToken, parseCheckboxToken } from '../../packages/markdown-parser/src/parser/inline-parsers/checkbox-parser'
+
+describe('checkbox inline parser', () => {
+  it('parses checkbox token from meta.checked true', () => {
+    const token: any = { meta: { checked: true } }
+    const node = parseCheckboxToken(token)
+    expect(node.type).toBe('checkbox')
+    expect(node.checked).toBe(true)
+    expect(node.raw).toBe('[x]')
+  })
+
+  it('parses checkbox input token from attrGet', () => {
+    const token: any = {
+      attrGet: (name: string) => {
+        if (name === 'checked')
+          return 'true'
+        return null
+      },
+    }
+    const node = parseCheckboxInputToken(token)
+    expect(node.type).toBe('checkbox_input')
+    expect(node.checked).toBe(true)
+    expect(node.raw).toBe('[x]')
+  })
+})