fix(card-sorting): match game selector background to other games

Change card sorting game gradient from bright teal (teal-200 to teal-300)
to softer pastel teal (teal-100 to teal-200) to match the lighter gradient
style used by other arcade games (Memory Lightning, Matching Pairs).

Updated gradient: linear-gradient(135deg, #ccfbf1, #99f6e4)

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

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

apps/web/src/arcade-games/card-sorting/index.ts

@@ -25,7 +25,7 @@ const manifest: GameManifest = {
   difficulty: 'Intermediate',
   chips: ['🧠 Pattern Recognition', '🎯 Solo Challenge', '📊 Smart Scoring'],
   color: 'teal',
-  gradient: 'linear-gradient(135deg, #99f6e4, #5eead4)',
+  gradient: 'linear-gradient(135deg, #ccfbf1, #99f6e4)',
   borderColor: 'teal.200',
   available: true,
 }