Replace Promise.resolve() with vi.waitFor in PTY claim test

Wait explicitly for the providerSpawn call to be made using vi.waitFor()
instead of relying on event-loop yielding. This makes the test more
deterministic and reduces flakiness from timing assumptions.

src/main/ipc/pty-pane-claim-arbitration.test.ts

@@ -505,9 +505,7 @@ describe('registerPtyHandlers', () => {
         ORCA_WORKTREE_ID: 'repo-1::/tmp'
       }
     }) as Promise<{ id: string }>
-    await Promise.resolve()
-
-    expect(providerSpawn).toHaveBeenCalledTimes(1)
+    await vi.waitFor(() => expect(providerSpawn).toHaveBeenCalledTimes(1))
     resolveSpawn({ id: 'pty-shared' })
     await expect(Promise.all([runtimeSpawn, rendererSpawn])).resolves.toEqual([
       { id: 'pty-shared' },