Establishes :root CSS custom properties (accent, surfaces, status, focus
ring) and applies the focus ring to inputs/buttons via :focus-visible.
Adds .req-pill class used by Task 4 to replace the bare-asterisk required
marker. Existing .label .req kept for backward compatibility during the
migration window.
Plan 2026-04-30 fullscreen UX phase 1 task 2.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>