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/markdown-parser/test/strong-math-streaming-no-hang.test.ts

@@ -0,0 +1,27 @@
+import { describe, expect, it } from 'vitest'
+import { getMarkdown, parseMarkdownToStructure } from '../src'
+
+describe('parseMarkdownToStructure - streaming strong+math', () => {
+  it('does not hang on unclosed strong ending with a closed $...$ span', { timeout: 500 }, () => {
+    const md = getMarkdown('stream-strong-math')
+    const markdown = '> **给定输入 $ x $'
+
+    expect(() => parseMarkdownToStructure(markdown, md)).not.toThrow()
+
+    // Simulate streaming: repeatedly parse progressive prefixes.
+    for (let i = 1; i <= markdown.length; i++) {
+      const chunk = markdown.slice(0, i)
+      expect(() => parseMarkdownToStructure(chunk, md)).not.toThrow()
+    }
+  })
+
+  it('does not recurse forever when a streaming strong prefix ends right before math opener content', { timeout: 500 }, () => {
+    const md = getMarkdown('stream-strong-heading-math')
+    const markdown = '### 1. **理解 \\\\(\\\\boldsymbol{alpha}^T \\\\boldsymbol{\\\\beta} = 0\\\\) 的含义**'
+
+    for (let i = 1; i <= markdown.length; i++) {
+      const chunk = markdown.slice(0, i)
+      expect(() => parseMarkdownToStructure(chunk, md, { final: false })).not.toThrow()
+    }
+  })
+})