The macOS window frame (transparent title bar, 38px) and the sidebar
share the same background color (#F7F6F3), making them visually
indistinguishable. Replace the sidebar's paddingTop: 38 with a
dedicated spacer div that has a bottom border (1px solid var(--border)),
matching the border style used between all other panels. The spacer
also serves as a drag region for window movement.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
