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/html-block-br-splitting.test.ts

@@ -0,0 +1,22 @@
+import { getMarkdown, parseMarkdownToStructure } from 'stream-markdown-parser'
+import { describe, expect, it } from 'vitest'
+
+describe('html_block split after <br/>', () => {
+  it('parses <br/> as a standalone html_block and keeps following paragraph separate', () => {
+    const tags = ['thinking']
+    const md = getMarkdown('html-block-br-splitting', { customHtmlTags: tags })
+    const markdown = `<br/>
+
+The easiest way to start the Dify server is through [Docker Compose](docker/docker-compose.yaml). Before running Dify with the following commands, make sure that [Docker](https://docs.docker.com/get-docker/) and [Docker Compose](https://docs.docker.com/compose/install/) are installed on your machine:`
+
+    const nodes = parseMarkdownToStructure(markdown, md, { customHtmlTags: tags }) as any[]
+
+    expect(nodes.length).toBeGreaterThanOrEqual(2)
+    expect(nodes[0].type).toBe('html_block')
+    expect(nodes[0].tag).toBe('br')
+    expect(String(nodes[0].raw ?? '').trim()).toBe('<br/>')
+
+    expect(nodes[1].type).toBe('paragraph')
+    expect(String(nodes[1].raw ?? '')).toContain('The easiest way to start the Dify server')
+  })
+})