feat: add kmenu icon for mobile

islands/KMenuButton.tsx

@@ -0,0 +1,14 @@
+import { Button } from "@components/Button.tsx";
+import { IconMenu2 } from "@components/icons.tsx";
+import { isKMenuOpen } from "@lib/kmenu.ts";
+
+export default function KMenuButton() {
+  return (
+    <Button
+      class="fixed bottom-4 right-4 md:hidden bg-gray-800 text-white p-3 rounded-full shadow-lg z-50"
+      onClick={() => (isKMenuOpen.value = true)}
+    >
+      <IconMenu2 class="w-6 h-6" />
+    </Button>
+  );
+}