Dashboard:
- Primary action (new registration) is now a full-width hero card
- Secondary actions are a compact 2x2 icon grid

Registration wizard:
- Mobile step indicator: compact progress bar + step name instead of
  cramped 5-circle stepper
- Sticky bottom nav bar on mobile (fixed position, safe-area aware)
  so Back/Next are always reachable without scrolling
- Activity selection uses horizontal scrollable pills on mobile
- Desktop layout remains unchanged (sm: breakpoint gates all changes)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>