Refactor Register page components

Splits the Register page into smaller, more manageable components for better organization and maintainability.

src/components/auth/RegisterHeader.tsx

@@ -0,0 +1,13 @@
+
+import React from "react";
+
+const RegisterHeader: React.FC = () => {
+  return (
+    <div className="text-center mb-8">
+      <h1 className="text-3xl font-bold text-neuro-income mb-2">젤리의 적자탈출</h1>
+      <p className="text-gray-500">새 계정을 만들고 재정 관리를 시작하세요</p>
+    </div>
+  );
+};
+
+export default RegisterHeader;