Prepare for easier shadcn ui install (#66469)

### What?
Installing shadcn/ui after installing this example was a bad experience.
Running `npx shadcn-ui@latest init` overwrites existing files causing
errors and a confusing start.
 
This allows a installing shadcn/ui without these issues.

Co-authored-by: Sam Ko <sam@vercel.com>

examples/with-supabase/app/globals.css

@@ -25,18 +25,3 @@
     @apply border-foreground/20;
   }
 }
-
-.animate-in {
-  animation: animateIn 0.3s ease 0.15s both;
-}
-
-@keyframes animateIn {
-  from {
-    opacity: 0;
-    transform: translateY(10px);
-  }
-  to {
-    opacity: 1;
-    transform: translateY(0);
-  }
-}

examples/with-supabase/app/login/page.tsx

@@ -74,7 +74,7 @@ export default function Login({
         Back
       </Link>
 
-      <form className="animate-in flex-1 flex flex-col w-full justify-center gap-2 text-foreground">
+      <form className="flex-1 flex flex-col w-full justify-center gap-2 text-foreground">
         <label className="text-md" htmlFor="email">
           Email
         </label>

examples/with-supabase/app/page.tsx

@@ -28,7 +28,7 @@ export default async function Index() {
         </div>
       </nav>
 
-      <div className="animate-in flex-1 flex flex-col gap-20 opacity-0 max-w-4xl px-3">
+      <div className="flex-1 flex flex-col gap-20 max-w-4xl px-3">
         <Header />
         <main className="flex-1 flex flex-col gap-6">
           <h2 className="font-bold text-4xl mb-4">Next steps</h2>

examples/with-supabase/app/protected/page.tsx

@@ -31,7 +31,7 @@ export default async function ProtectedPage() {
         </nav>
       </div>
 
-      <div className="animate-in flex-1 flex flex-col gap-20 opacity-0 max-w-4xl px-3">
+      <div className="flex-1 flex flex-col gap-20 max-w-4xl px-3">
         <Header />
         <main className="flex-1 flex flex-col gap-6">
           <h2 className="font-bold text-4xl mb-4">Next steps</h2>