Mobile & responsive polish
Registry item cards now scale intelligently with the items-per-row setting, the site nav meets touch-target standards, and mobile layouts across the registry are fully cleaned up.
- ItemCard scales with column count — compact padding + smaller text at 4 col; buttons stack, description hidden, labels shortened at 5 col
- Correct next/image sizes hint per column count — browser fetches the right image variant
- "I bought this" → "Bought" and "Buy now" → "Buy" at 5-col ultra-compact
- Owner action bar scrolls horizontally on mobile instead of wrapping to two lines
- Mobile category filter pills scroll horizontally instead of stacking vertically
- Sidebar sticky offset corrected — no longer overlaps the owner action bar
- Nav hover states use CSS hover: instead of JS onMouseEnter/Leave — now works on touch devices
- All nav links meet 44px touch target minimum (WCAG 2.5.5)
- no-scrollbar CSS utility added — was used but never defined (silent scroll failure on mobile)
- Missing exchangeRate/displayCurrency props fixed on inner category card loop