Add storefront component migration: cards, badges, progress bars, animations, and React wrapper package

Major feature migration from dt-shopify-storefront into the design system:

- Card system: per-card color modes (normal/emphasis/warning/success/other),
  progress bars, full-bleed card body (card-body-flush), image bevel clip-paths,
  and visible structural borders at bevel corners
- Badge system: dt-card-badge with position-aware offsets for cards vs media frames
- Media frames: dt-bevel-media with inner surface fill, image clipping, and
  "MISSING MEDIA" placeholder for empty containers
- Interactive bevel buttons: dt-btn with hover/selected states and pulse animation
- Menu items: dt-menu-item with active states and level indentation
- Animations: scale-in, fade-in, slide-up, pulse, ping, spin keyframes
- Feature legend: CSS grid for product feature icons with state colors
- Scrollbar styling for DT brand
- New @dangerousthings/react package wrapping web CSS components
- New @dangerousthings/tailwind-preset package
- New @dangerousthings/hex-background package
- Desktop showcase rewritten in React with Tailwind CSS
- Mobile showcase updated with new screens (animations, filters, advanced cards)
- Tokens: added mode color tokens, RGB variants, and selected-state tokens

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/showcase/mobile/src/screens/HomeScreen.tsx

@@ -56,6 +56,27 @@ const categories: {
     route: 'Overlays',
     count: 5,
   },
+  {
+    title: 'ADVANCED CARDS',
+    subtitle: 'Selected state, progress bar, badge overlays, stagger',
+    mode: 'emphasis',
+    route: 'CardsAdvanced',
+    count: 4,
+  },
+  {
+    title: 'ANIMATIONS',
+    subtitle: 'DTStaggerContainer, useScaleIn, usePulse',
+    mode: 'success',
+    route: 'Animations',
+    count: 3,
+  },
+  {
+    title: 'FILTERS & FEATURES',
+    subtitle: 'DTFeatureLegend, DTMobileFilterOverlay',
+    mode: 'other',
+    route: 'Filters',
+    count: 2,
+  },
   {
     title: 'THEME REFERENCE',
     subtitle: 'Colors, Typography, Spacing',