[Feature] Shop UI redesign — featured items, hover effects, improved discovery

## Overview
Current shop UI needs a redesign to drive conversion. Featured items section, hover/preview effects on territory skins, and cleaner product discovery.

## Scope
- Featured items section at top of shop (pinned editorial slot, admin configurable)
- Hover/preview effect on territory skins (show pattern applied to territory on mouse-over)
- Category navigation (feeds into store categories issue)
- New releases section
- Sale / limited edition section
- Mobile-responsive

## Acceptance criteria
- [ ] Featured slot configurable by admin
- [ ] Hover/preview shows pattern applied to territory on mouse-over
- [ ] Category navigation functional
- [ ] Shop loads in under 2 seconds
- [ ] Fully mobile-responsive

## Notes
This is a dependency for most other cosmetics issues — shop redesign should be prioritised early in the monetisation sprint.