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/fence-trailing-backtick.test.ts

@@ -0,0 +1,30 @@
+import { parseFenceToken } from 'stream-markdown-parser'
+import { describe, expect, it } from 'vitest'
+
+describe('fence parser trailing fence cleanup', () => {
+  it('removes a trailing line that only contains backticks from token.content', () => {
+    const token: any = {
+      type: 'fence',
+      info: 'ts',
+      content: 'const a = 1\n```',
+      map: [0, 2],
+    }
+
+    const node = parseFenceToken(token as any)
+    expect(node).toBeDefined()
+    expect((node as any).code).toBe('const a = 1')
+    expect((node as any).raw).toBe('const a = 1')
+  })
+
+  it('keeps legitimate content that contains backticks not on their own line', () => {
+    const token: any = {
+      type: 'fence',
+      info: 'text',
+      content: 'console.log(\'`inline`)\n', // backtick inside code, not a fence line
+      map: [0, 2],
+    }
+    const node = parseFenceToken(token as any)
+    expect((node as any).code).toBe('console.log(\'`inline`)\n')
+    expect((node as any).raw).toBe('console.log(\'`inline`)\n')
+  })
+})