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/list-item-streaming-fade.test.ts

@@ -0,0 +1,28 @@
+import { mount } from '@vue/test-utils'
+import { describe, expect, it } from 'vitest'
+import NodeRenderer from '../src/components/NodeRenderer'
+import { flushAll } from './setup/flush-all'
+
+describe('list item streaming fade', () => {
+  it('replays appended-text fade inside list items', async () => {
+    const wrapper = mount(NodeRenderer, {
+      props: {
+        batchRendering: false,
+        content: '- Hello',
+      },
+    })
+
+    await flushAll()
+
+    await wrapper.setProps({
+      content: '- HelloWorld',
+    })
+    await flushAll()
+
+    const listItem = wrapper.get('li.list-item')
+    const delta = wrapper.get('li.list-item .text-node-stream-delta')
+
+    expect(delta.text()).toBe('World')
+    expect(listItem.text()).toContain('HelloWorld')
+  })
+})