feat(web): add smooth page transitions and WASM loading states

- Implement navigation state tracking with optimistic UI updates
- Add loading spinner and error handling for WASM initialization
- Insert browser yield points during game initialization to prevent freezing
- Redesign leaderboard with tabbed navigation and mock data structure
- Add utility CSS classes for consistent page layouts

web/pages/download/+Page.tsx

@@ -1,12 +1,10 @@
 export default function Page() {
   return (
-    <div className="mx-auto max-w-3xl py-8 px-4">
+    <div className="page-container">
       <div className="space-y-6">
-        <div className="border border-yellow-400/20 rounded-md bg-transparent p-6 shadow-[0_4px_20px_rgba(250,204,21,0.08)]">
+        <div className="card">
           <h2 className="text-2xl font-bold mb-4">Download Pac-Man</h2>
-          <p className="text-gray-300 mb-4">
-            Download instructions and releases will be available here soon.
-          </p>
+          <p className="text-gray-300 mb-4">Download instructions and releases will be available here soon.</p>
         </div>
       </div>
     </div>