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/components/DTButton.tsx

@@ -0,0 +1,66 @@
+/**
+ * DTButton — Interactive bevel button with mode colors.
+ *
+ * CSS reference: bevels.css .dt-btn, .btn-primary, .mode-*, .selected
+ */
+
+import type { ReactNode, CSSProperties, MouseEvent } from 'react';
+import type { DTVariant } from '@dangerousthings/tokens';
+import { cx } from '../utils/cx';
+import { getVariantClass } from '../utils/variantClasses';
+
+interface DTButtonProps {
+  children: ReactNode;
+  /** Color variant @default 'normal' */
+  variant?: DTVariant;
+  /** Display mode @default 'outlined' */
+  mode?: 'outlined' | 'contained';
+  /** Persistent selected state (bevel + 70% fill) */
+  selected?: boolean;
+  onClick?: (e: MouseEvent<HTMLButtonElement>) => void;
+  disabled?: boolean;
+  type?: 'button' | 'submit' | 'reset';
+  className?: string;
+  style?: CSSProperties;
+}
+
+export function DTButton({
+  children,
+  variant = 'normal',
+  mode = 'outlined',
+  selected = false,
+  onClick,
+  disabled = false,
+  type = 'button',
+  className,
+  style,
+}: DTButtonProps) {
+  if (mode === 'contained') {
+    return (
+      <button
+        className={cx('btn-primary', getVariantClass(variant), className)}
+        onClick={onClick}
+        disabled={disabled}
+        type={type}
+        style={style}>
+        {children}
+      </button>
+    );
+  }
+
+  return (
+    <button
+      className={cx(
+        'dt-btn',
+        getVariantClass(variant),
+        selected && 'selected',
+        className,
+      )}
+      onClick={onClick}
+      disabled={disabled}
+      type={type}
+      style={style}>
+      {children}
+    </button>
+  );
+}