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/DTAccordion.tsx

@@ -0,0 +1,83 @@
+/**
+ * DTAccordion — Expandable sections with animated height and chevron.
+ *
+ * CSS reference: forms-dt.css .dt-accordion, .dt-accordion-header,
+ * .dt-accordion-chevron, .dt-accordion-content
+ */
+
+import { useState, useCallback, type ReactNode, type CSSProperties } from 'react';
+import type { DTVariant } from '@dangerousthings/tokens';
+import { cx } from '../utils/cx';
+
+export interface DTAccordionSection {
+  key: string;
+  title: string;
+  children: ReactNode;
+}
+
+interface DTAccordionProps {
+  sections: DTAccordionSection[];
+  /** Header variant when closed @default 'normal' */
+  variant?: DTVariant;
+  /** Header variant when open @default 'emphasis' */
+  activeVariant?: DTVariant;
+  /** Allow multiple sections open @default false */
+  allowMultiple?: boolean;
+  initialOpenKeys?: string[];
+  onSectionToggle?: (key: string, isOpen: boolean) => void;
+  className?: string;
+  style?: CSSProperties;
+}
+
+export function DTAccordion({
+  sections,
+  allowMultiple = false,
+  initialOpenKeys,
+  onSectionToggle,
+  className,
+  style,
+}: DTAccordionProps) {
+  const [openKeys, setOpenKeys] = useState<Set<string>>(
+    new Set(initialOpenKeys),
+  );
+
+  const toggle = useCallback(
+    (key: string) => {
+      setOpenKeys(prev => {
+        const next = new Set(allowMultiple ? prev : []);
+        const isOpening = !prev.has(key);
+        if (isOpening) next.add(key);
+        else next.delete(key);
+        onSectionToggle?.(key, isOpening);
+        return next;
+      });
+    },
+    [allowMultiple, onSectionToggle],
+  );
+
+  return (
+    <div className={cx('dt-accordion', className)} style={style}>
+      {sections.map(section => {
+        const isOpen = openKeys.has(section.key);
+        return (
+          <div key={section.key}>
+            <button
+              className="dt-accordion-header"
+              aria-expanded={isOpen}
+              onClick={() => toggle(section.key)}
+              type="button"
+              style={{ width: '100%' }}>
+              <span>{section.title}</span>
+              <span className="dt-accordion-chevron" />
+            </button>
+            <div
+              className="dt-accordion-content"
+              data-open={isOpen}>
+              {section.children}
+            </div>
+          </div>
+        );
+      })}
+    </div>
+  );
+}