feat(down-button): added down button func

Now you don't have to scroll all the way down yay

web-app/src/components/ui/button/down-button.jsx

@@ -3,9 +3,17 @@ import { ArrowDown } from "lucide-react";
 import { motion } from "motion/react";
 
 export default function DownButton({ onClick }) {
+  function handleClick(e) {
+    if (onClick) return onClick(e);
+    // default behavior: scroll to bottom of page smoothly
+    const doc = document.documentElement;
+    const top = Math.max(doc.scrollHeight, document.body.scrollHeight);
+    window.scrollTo({ top, behavior: "smooth" });
+  }
+
   return (
     <motion.button
-      onClick={onClick}
+      onClick={handleClick}
       className="bg-gray-700 p-2 rounded-2xl file-input border-2 border-gray-600 size-10"
       whileHover={{ scale: 1.1 }}
       whileTap={{ scale: 0.9 }}