feat: add Header component

Author: yeonjuan

src/components/Header.tsx

@@ -0,0 +1,9 @@
+import React from "react";
+import type { FC } from "react";
+import "@/css/header.css";
+
+export const Header: FC = () => (
+  <header>
+    <h2 style={{ color: "#666" }}>TypeScript ESlint Demo</h2>
+  </header>
+);