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/optional-monaco.test.ts

@@ -0,0 +1,30 @@
+import { describe, expect, it } from 'vitest'
+
+describe('optional monaco dependency', () => {
+  it('should handle missing stream-monaco gracefully', async () => {
+    // Dynamically import the monaco module
+    const { getUseMonaco } = await import('../src/components/CodeBlockNode/monaco')
+
+    // Mock the import to simulate missing package
+    // In a real scenario where stream-monaco is not installed,
+    // the import will fail and getUseMonaco should return null
+    // This test verifies the function exists and can be called
+    const result = await getUseMonaco()
+
+    // If stream-monaco is installed (as it is in the dev environment),
+    // result will be the module. If not installed, result will be null.
+    // The important thing is that no error is thrown.
+    expect(typeof result === 'object' || result === null).toBe(true)
+  })
+
+  it('should cache the import result', async () => {
+    const { getUseMonaco } = await import('../src/components/CodeBlockNode/monaco')
+
+    // Call twice to test caching
+    const result1 = await getUseMonaco()
+    const result2 = await getUseMonaco()
+
+    // Both calls should return the same result (either the module or null)
+    expect(result1).toBe(result2)
+  })
+})