Refactor: Split Index page

Refactor Index.tsx into smaller, more manageable components.

src/components/Header.tsx

@@ -0,0 +1,21 @@
+
+import React from 'react';
+import { Bell } from 'lucide-react';
+
+const Header: React.FC = () => {
+  return (
+    <header className="py-8">
+      <div className="flex justify-between items-center">
+        <div>
+          <h1 className="text-2xl font-bold neuro-text">반갑습니다</h1>
+          <p className="text-gray-500">젤리의 적자탈출</p>
+        </div>
+        <button className="neuro-flat p-2.5 rounded-full">
+          <Bell size={20} className="text-gray-600" />
+        </button>
+      </div>
+    </header>
+  );
+};
+
+export default Header;