style(auth): improve auth page layout for mobile viewports

- use `min-h-dvh`, `flex-col`, and top-aligned justify on small screens in AuthPage
- add `mx-auto` to all auth page cards for consistent centering

src/features/auth/AuthPage.server.js

@@ -14,7 +14,7 @@ export default async function AuthPage({ params, searchParams }) {
   const session = await getSession();
 
   return (
-    <div className="min-h-screen flex items-center justify-center p-4 md:p-8 bg-neutral-50 dark:bg-black">
+    <div className="min-h-dvh flex flex-col items-center justify-start sm:justify-center px-4 py-10 sm:py-8 md:p-8 bg-neutral-50 dark:bg-black">
       <div className="max-w-md w-full">
         <AuthPageClient
           params={params}