Keep sidebar description cards to keyboard focus and inside the window

Focus only opens a tooltip when it is focus-visible, so tapping a row on
touch no longer shows its card. The right-side card clamps vertically to
the viewport, Escape keeps the focused control's tooltip dismissed until
focus moves, and the remaining raw sizes use spacing tokens.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>