feat: add standalone Nim game page, route, and container layout; remove global header/footer from /games/nim

src/pages/NimGamePage.tsx

@@ -0,0 +1,12 @@
+import React from 'react';
+import NimGame from '@/components/NimGame';
+
+const NimGamePage = () => {
+  return (
+    <div className="container mx-auto px-4 py-8">
+      <NimGame />
+    </div>
+  );
+};
+
+export default NimGamePage;