Implement user authentication

Implement login functionality and user authentication logic.

src/components/Header.tsx

@@ -1,13 +1,20 @@
 
 import React from 'react';
 import { Bell } from 'lucide-react';
+import { useAuth } from '@/contexts/AuthContext';
 
 const Header: React.FC = () => {
+  const { user } = useAuth();
+  
+  const userName = user?.user_metadata?.username || '익명';
+  
   return (
     <header className="py-8">
       <div className="flex justify-between items-center">
         <div>
-          <h1 className="text-2xl font-bold neuro-text">반갑습니다</h1>
+          <h1 className="text-2xl font-bold neuro-text">
+            {user ? `${userName}님, 반갑습니다` : '반갑습니다'}
+          </h1>
           <p className="text-gray-500">젤리의 적자탈출</p>
         </div>
         <button className="neuro-flat p-2.5 rounded-full">