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/react/src/hooks/usePulse.ts

@@ -0,0 +1,24 @@
+/**
+ * Hook: toggles dt-animate-pulse CSS class based on enabled flag.
+ */
+import { useEffect } from 'react';
+
+export function usePulse(
+  ref: React.RefObject<HTMLElement | null>,
+  enabled = false,
+): void {
+  useEffect(() => {
+    const el = ref.current;
+    if (!el) return;
+
+    if (enabled) {
+      el.classList.add('dt-animate-pulse');
+    } else {
+      el.classList.remove('dt-animate-pulse');
+    }
+
+    return () => {
+      el.classList.remove('dt-animate-pulse');
+    };
+  }, [ref, enabled]);
+}