fix: kidlisp.com context menu renders on top of everything
Replace ::before pseudo-element outlines with box-shadow inset,
which renders as part of the background layer and never covers
descendant content like Monaco's context menu. Remove the
z-index: 0 stacking context that was trapping the menu.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>