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/stream-monaco/test/scroll.test.ts

@@ -0,0 +1,39 @@
+import { describe, expect, it } from 'vitest'
+import { createScrollWatcherForEditor } from '../src/utils/scroll'
+
+describe('createScrollWatcherForEditor', () => {
+  it('calls onPause when delta < 0 and onMaybeResume otherwise', () => {
+    let paused = false
+    let resumed = false
+    let last = 50
+    const editor = (() => {
+      let handler: ((e: any) => void) | null = null
+      return {
+        getScrollTop() { return last },
+        onDidScrollChange(cb: (e: any) => void) {
+          handler = cb
+          return {
+            dispose() {
+              handler = null
+            },
+          }
+        },
+        // helper to simulate
+        __emit(e: any) { handler?.(e) },
+      }
+    })()
+    const disp = createScrollWatcherForEditor(editor as any, {
+      onPause: () => { paused = true },
+      onMaybeResume: () => { resumed = true },
+      getLast: () => last,
+      setLast: (v: number) => { last = v },
+    })
+    // simulate up scroll (delta < 0)
+    editor.__emit({ scrollTop: 40 })
+    expect(paused).toBe(true)
+    // simulate down scroll
+    editor.__emit({ scrollTop: 100 })
+    expect(resumed).toBe(true)
+    disp?.dispose?.()
+  })
+})