feat(design-system): page /design-system dev-only — palette live + composants (Sprint 0.5 étape 7)

src/app/router.tsx

@@ -1,9 +1,24 @@
+import React, { Suspense } from 'react'
 import { Routes, Route } from 'react-router-dom'
 
+const DesignSystemPage = import.meta.env.DEV
+  ? React.lazy(() => import('@/features/design-system/DesignSystemPage'))
+  : () => null
+
 export function AppRouter() {
   return (
     <Routes>
       <Route path="/" element={<ScaffoldPlaceholder />} />
+      {import.meta.env.DEV && (
+        <Route
+          path="/design-system"
+          element={
+            <Suspense fallback={<div className="p-6 text-ink-4">Loading…</div>}>
+              <DesignSystemPage />
+            </Suspense>
+          }
+        />
+      )}
     </Routes>
   )
 }