feat(site): consistent card radius and remove duplicate login CTAs

Professional tidy-up of the landing experience:
- SurfaceCard: unified rounded-xl radius for a crisper, consistent look.
- Hero: matches the new card radius and gains a dual-direction title
  shadow so the headline stays readable over the header artwork.
- Login/register: drop the duplicated "no account / have an account"
  paragraphs — the forms already ship an inline footer, so one clear CTA
  cluster remains and the side column is cleaner.

src/components/surface-card.tsx

@@ -48,7 +48,7 @@ export function SurfaceCard({
 
 	return (
 		<div
-			className={`surface-card card-hairline overflow-hidden rounded-2xl border bg-[var(--color-surface)] ${className}`}
+			className={`surface-card card-hairline overflow-hidden rounded-xl border bg-[var(--color-surface)] ${className}`}
 			style={{
 				borderColor: CARD_BORDER,
 				boxShadow: CARD_SHADOW,