Accessibility improvements for bottom drawer and sidebar overlay

[tomusdrw]

Bottom drawer

• Add focus trap when expanded (currently focus can escape behind the drawer)
• Add `aria-expanded` attribute to the handle button
• Consider adding `aria-label="Toggle sidebar drawer"` to the handle button

Sidebar overlay

• Add focus trap when open
• Add `role="dialog"` and `aria-modal="true"` to the panel
• Auto-focus the close button when opening
• Escape key dismiss is already implemented

Split pane header

• Version dropdown and 3-dots menu should have `aria-label` attributes
• The floating header should be announced to screen readers

Generated with Claude Code