Migrate sidebar to use Tailwind/Shadcn

src/components/AppHeader.tsx

@@ -0,0 +1,11 @@
+export default function AppHeader() {
+
+  return (
+    <header className="absolute flex items-center justify-between px-4 py-2 border-b bg-background">
+      <div className="flex items-center gap-2 text-muted-foreground">
+        <Book className="h-5 w-5" />
+      </div>
+
+    </header>
+  )
+}