fix(homepage): display gradient backgrounds on all game cards

Fixed issue where only the Memory Lightning card showed its gradient
background while other cards appeared dark. The problem was that Panda
CSS's css() function doesn't properly handle raw CSS gradient strings.

Solution: Moved gradient from Panda css() to inline style prop, allowing
all four game cards to display their vibrant gradients:
- Memory Lightning: purple/violet
- Matching Pairs: pink/red
- Complement Race: blue/cyan
- Card Sorting: green/cyan

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

apps/web/src/app/page.tsx

@@ -609,8 +609,8 @@ function GameCard({
   return (
     <Link href={href}>
       <div
+        style={{ background: gradient }}
         className={css({
-          background: gradient,
           rounded: 'xl',
           p: '6',
           shadow: 'lg',