Migrate from Vue2 to React with modern tech stack

- Replace Vue2 + Vue CLI with Vite + React 18 + TypeScript
- Add Tailwind CSS for efficient styling
- Implement clean component architecture:
  - Split 1000+ line Vue component into focused React components
  - Add proper type safety with TypeScript
  - Use React Query for efficient data fetching
- Update GitHub Actions for React build pipeline
- Maintain existing functionality and design
- Support Node.js 23 with .nvmrc

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/components/pages/UserPage.tsx

@@ -0,0 +1,50 @@
+import { useParams } from 'react-router-dom';
+import { useQuery } from '@tanstack/react-query';
+import Navigation from '../common/Navigation';
+import CardGrid from '../card/CardGrid';
+import UserProfile from '../user/UserProfile';
+import { fetchUsers, fetchUserCards } from '../../utils/api';
+
+export default function UserPage() {
+  const { username } = useParams<{ username: string }>();
+  
+  const { data: users } = useQuery({
+    queryKey: ['users'],
+    queryFn: () => fetchUsers(),
+  });
+
+  const user = users?.data.find(u => u.username === username);
+  
+  const { data: cards, isLoading: cardsLoading } = useQuery({
+    queryKey: ['userCards', user?.id],
+    queryFn: () => fetchUserCards(user!.id),
+    enabled: !!user?.id,
+  });
+
+  if (!user) {
+    return (
+      <div className="min-h-screen">
+        <Navigation />
+        <div className="max-w-6xl mx-auto px-4 py-8">
+          <div className="text-center text-xl">User not found</div>
+        </div>
+      </div>
+    );
+  }
+
+  return (
+    <div className="min-h-screen">
+      <Navigation username={username} />
+      
+      <div className="max-w-6xl mx-auto px-4">
+        <UserProfile user={user} cards={cards?.data || []} />
+        
+        {cardsLoading ? (
+          <div className="text-center py-8">Loading cards...</div>
+        ) : (
+          <CardGrid cards={cards?.data || []} user={user} />
+        )}
+      </div>
+    </div>
+  );
+}