[Nebula] Add deprecation banner with migration information

Author: joaquim-verges

apps/nebula/src/app/login/NebulaLoginPage.tsx

@@ -81,6 +81,15 @@ export function NebulaLoggedOutStatePage(props: {
         </div>
       </header>
 
+      {/* Deprecation banner */}
+      <div className="container bg-destructive p-6">
+          <div className="text-md text-destructive-foreground">
+            <h4 className="font-bold text-lg">Nebula is now <Link className="underline text-destructive-foreground hover:text-destructive-foreground/80" href="https://thirdweb.com/ai" target="_blank">thirdweb AI</Link> and will be deprecated on September 30, 2025.</h4> 
+            <p>To continue using thirdweb AI, please sign in to the <Link className="underline text-destructive-foreground hover:text-destructive-foreground/80" href="https://thirdweb.com/login" target="_blank">thirdweb dashboard</Link> and create a new project.</p>
+            <p>If you have any funds left in your Nebula account, please withdraw them before September 30, 2025.</p>
+          </div>
+        </div>
+
       {showPage === "connect" && (
         <NebulaLoginPage redirectPath={`/?${redirectPathParams}`} />
       )}