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/math-inline-code-span-regression.test.ts

@@ -0,0 +1,58 @@
+import { getMarkdown, parseMarkdownToStructure } from 'stream-markdown-parser'
+import { describe, expect, it } from 'vitest'
+
+function walk(value: unknown, visit: (node: any) => void, seen = new WeakSet<object>()) {
+  if (!value || typeof value !== 'object')
+    return
+  if (seen.has(value))
+    return
+  seen.add(value)
+
+  if (Array.isArray(value)) {
+    for (const item of value)
+      walk(item, visit, seen)
+    return
+  }
+
+  const node = value as any
+  if (typeof node.type === 'string')
+    visit(node)
+
+  for (const child of Object.values(node))
+    walk(child, visit, seen)
+}
+
+describe('math inline should not break inline code spans', () => {
+  const md = getMarkdown('math-inline-code-span-regression')
+  const input = '`$...$`， `\\(...\\)`'
+
+  it('keeps markdown-it inline tokens as code_inline', () => {
+    const tokens = md.parse(input, {})
+    const inline = tokens.find((t: any) => t.type === 'inline')
+    const children = (inline?.children ?? []) as any[]
+
+    const mathChildren = children.filter(c => c.type === 'math_inline')
+    const codeChildren = children.filter(c => c.type === 'code_inline')
+
+    expect(mathChildren).toHaveLength(0)
+    expect(codeChildren).toHaveLength(2)
+    expect(codeChildren[0].content).toBe('$...$')
+    expect(codeChildren[1].content).toBe('\\(...\\)')
+  })
+
+  it('keeps structured nodes as inline_code and preserves backslashes', () => {
+    const nodes = parseMarkdownToStructure(input, md)
+    const codes: string[] = []
+    let mathCount = 0
+
+    walk(nodes, (node) => {
+      if (node.type === 'inline_code')
+        codes.push(String(node.code ?? ''))
+      if (node.type === 'math_inline')
+        mathCount++
+    })
+
+    expect(mathCount).toBe(0)
+    expect(codes).toEqual(['$...$', '\\(...\\)'])
+  })
+})