add required pattern for guest name

client/src/components/auth/AuthModal.tsx

@@ -62,6 +62,8 @@ export default function AuthModal() {
                 <span>Name</span>
                 <input
                   type="text"
+                  pattern="[A-Za-z0-9_]+"
+                  title="Alphanumeric characters and underscores only"
                   id="guestName"
                   name="guestName"
                   placeholder="Enter name here..."