chore: initial DSMMG v0.2 — refonte architecturale complète

Mise en place du Design System ManageMate Group v0.2 — refonte du
système de tokens (préfixe --mmg-color-*), 9 presets accent
user-themable validés WCAG AA, overlays Radix UI + Floating UI,
Storybook 8 + Vitest + axe-core en CI, doc Astro Starlight,
DESIGN.md (format google-labs-code) et exports tokens DTCG/CSS/
TS/Figma/Tailwind v3 et v4.

- 4 packages monorepo pnpm : @managemate/{tokens,css,react,icons}
- 62 composants React headless-first (Sheet, HoverCard, ContextMenu,
  Slider, ToggleGroup, AvatarGroup, UserCard, ProfileHeader,
  MetricCard, PricingCard, FeatureCard, Text/Display/Eyebrow/Lead…)
- Lint contraste WCAG : 37/37 paires AA, branché CI
- Toast pile Sonner-style avec ResizeObserver
- Theming user (9 presets) sans casser sémantique fixe
- Identité Synapse (rose #D12B6A) préservée

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/react/src/Accordion.tsx

@@ -0,0 +1,32 @@
+import { useId, useState, type ReactNode } from "react";
+import { cx } from "./utils";
+import { Icon } from "./Icon";
+
+export type AccordionProps = {
+  label: ReactNode;
+  defaultOpen?: boolean;
+  children: ReactNode;
+  className?: string;
+};
+
+export function Accordion({ label, defaultOpen = false, children, className }: AccordionProps) {
+  const [open, setOpen] = useState(defaultOpen);
+  const id = useId();
+  return (
+    <div className={cx("mmg-accordion", className)} data-open={open}>
+      <button
+        type="button"
+        className="mmg-accordion__btn"
+        aria-expanded={open}
+        aria-controls={id}
+        onClick={() => setOpen((v) => !v)}
+      >
+        <span>{label}</span>
+        <Icon name="arrow-down-line" className="mmg-accordion__chevron" />
+      </button>
+      <div id={id} role="region" className="mmg-accordion__panel">
+        {children}
+      </div>
+    </div>
+  );
+}