Add shadcn components, basic layout and default design

src/components/global/Header.tsx

@@ -0,0 +1,11 @@
+import ModeToggle from "./ModeToggle";
+import TopNav from "./TopNav";
+
+export default function Header() {
+  return (
+    <div className="flex items-center justify-between">
+      <TopNav />
+      <ModeToggle />
+    </div>
+  );
+}