Remove unsupported url option from the auth config

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/lib/auth.ts

@@ -75,7 +75,4 @@ export const authOptions: NextAuthOptions = {
     error: "/auth/error",
   },
   secret: process.env.NEXTAUTH_SECRET,
-  ...(process.env.NEXTAUTH_URL && {
-    url: process.env.NEXTAUTH_URL,
-  }),
 };