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/custom-html-block-repeat.test.ts

@@ -0,0 +1,45 @@
+import { getMarkdown, parseMarkdownToStructure } from 'stream-markdown-parser'
+import { describe, expect, it } from 'vitest'
+
+function normalizeText(input: string) {
+  return input.replace(/\s+/g, ' ').trim()
+}
+
+describe('custom html_block -> custom nodes repeat', () => {
+  it('parses repeated custom block tags with distinct content', () => {
+    const markdown = `<new-question>A</new-question>
+<sub-question>
+B
+</sub-question>
+
+<sub-question>
+C
+</sub-question>`
+
+    const tags = ['thinking', 'new-question', 'sub-question']
+    const md = getMarkdown('custom-html-block-repeat', { customHtmlTags: tags })
+
+    const nodes = parseMarkdownToStructure(markdown, md, { customHtmlTags: tags }) as any[]
+
+    // markdown-it tokenizes the first two lines as a paragraph (inline HTML), and the
+    // second <sub-question> as an html_block. The parser must NOT "re-extract" the
+    // earlier <sub-question> (B) when converting the later html_block (C).
+    expect(nodes).toHaveLength(2)
+
+    const paragraph = nodes[0]
+    expect(paragraph.type).toBe('paragraph')
+
+    const newQ = paragraph.children?.find((n: any) => n.type === 'new-question')
+    const subInline = paragraph.children?.find((n: any) => n.type === 'sub-question')
+
+    expect(newQ).toBeTruthy()
+    expect(normalizeText(String(newQ.content))).toBe('A')
+
+    expect(subInline).toBeTruthy()
+    expect(normalizeText(String(subInline.content))).toBe('B')
+
+    const subBlock = nodes[1]
+    expect(subBlock.type).toBe('sub-question')
+    expect(normalizeText(String(subBlock.content))).toBe('C')
+  })
+})