Adjust profile picture size

Adjusted the profile picture size to occupy the height of two lines.

src/components/Header.tsx

@@ -2,6 +2,7 @@
 import React from 'react';
 import { Bell } from 'lucide-react';
 import { useAuth } from '@/contexts/auth';
+import { Avatar, AvatarFallback, AvatarImage } from '@/components/ui/avatar';
 
 const Header: React.FC = () => {
   const {
@@ -11,23 +12,15 @@ const Header: React.FC = () => {
   
   return <header className="py-8">
       <div className="flex justify-between items-center">
-        <div>
-          <div className="flex items-center mb-1">
-            <img 
-              src="/zellyy.png" 
-              alt="Zellyy" 
-              className="w-6 h-6 mr-2"
-            />
+        <div className="flex items-center">
+          <Avatar className="h-12 w-12 mr-3">
+            <AvatarImage src="/zellyy.png" alt="Zellyy" />
+            <AvatarFallback>ZY</AvatarFallback>
+          </Avatar>
+          <div>
             <h1 className="text-2xl font-bold neuro-text">
               {user ? `${userName}님, 반갑습니다` : '반갑습니다'}
             </h1>
-          </div>
-          <div className="flex items-center">
-            <img 
-              src="/zellyy.png" 
-              alt="Zellyy" 
-              className="w-4 h-4 mr-2"
-            />
             <p className="text-gray-500 text-left">젤리의 적자탈출</p>
           </div>
         </div>