Refactor scratchpad from a flex-layout sidebar that pushes content left
to a floating overlay panel (position: fixed) that doesn't affect layout.
Panel slides in from the right with Ctrl+/ toggle. Main content adjusts
padding responsively when panel is open.
Also apply thin scrollbar styling globally across all scrollable elements
for a consistent, minimal look.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
