feat(nav): Make Login button a functional link

The Login button in the navigation bar was previously a static UI element. This commit converts it into a functional Next.js `<Link>` component.

The link now directs users to `https://app.opplens.com` and opens in a new tab (`target="_blank"`) to provide access to the application's login page. Additionally, a vertical margin has been added to the navigation bar for better spacing.

app/_components/NavigationBar.tsx

@@ -5,10 +5,15 @@ import { usePathname } from "next/navigation";
 const NavigationBar = () => {
   const pathname = usePathname();
   return (
-    <nav>
+    <nav className="my-5">
       <ul className="flex flex-row-reverse items-center gap-12">
-        <li className="bg-(--primary) text-white py-5 px-12 rounded-full">
+        <li>
+          <Link
+            href={"https://app.opplens.com"}
+            className="cursor-pointer bg-(--primary) text-white py-5 px-12 rounded-full"
+            target="_blank">
             Login
+          </Link>
         </li>
         <li>
           <Link