Fix window.setTimeout in integration test client

The prefer-window-timers auto-fix changed activeWindow.setTimeout to
window.setTimeout in client.ts, but client.ts runs in Node.js (not
Obsidian), where window is never defined. Revert to plain setTimeout,
which is a native Node.js global and is safe here since no-restricted-globals
is already suppressed for the integration test scope.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>