fix(desktop): import GatewayEvent type in the background.complete test

The salvaged test imported RpcEvent from @/types/hermes; main's event
type lives in @hermes/shared as GatewayEvent.

apps/desktop/src/app/session/hooks/use-message-stream/background-complete-event.test.tsx

@@ -1,7 +1,7 @@
 import { act, cleanup } from '@testing-library/react'
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 
-import type { RpcEvent } from '@/types/hermes'
+import type { GatewayEvent } from '@hermes/shared'
 
 import { type MessageStreamHarness, renderMessageStream } from './test-harness'
 
@@ -14,7 +14,7 @@ function mountStream() {
   stream = renderMessageStream(SID)
 }
 
-function emit(type: RpcEvent['type'], payload: RpcEvent['payload'] = {}, sessionId = SID) {
+function emit(type: GatewayEvent['type'], payload: GatewayEvent['payload'] = {}, sessionId = SID) {
   act(() => stream.handleEvent({ payload, session_id: sessionId, type }))
 }