refactor: remove old single-player memory-quiz version

Removed the original 2,071-line single-player implementation that has been
superseded by the modular arcade version.

**Deleted:**
- apps/web/src/app/games/memory-quiz/page.tsx (2,071 lines)
- Removed unused _handleGameClick function from /games page

**Kept (still in use):**
- /lib/memory-quiz-utils.ts - Shared utilities used by arcade version
- /lib/memory-quiz-utils.test.ts - Test coverage
- /arcade-games/memory-quiz/ - New modular arcade implementation
- /arcade/memory-quiz/ - Redirect page to arcade

**Verified:**
- Arcade version is completely independent (imports from @/arcade-games/memory-quiz)
- Arcade version uses shared utility (/lib/memory-quiz-utils.ts)
- No functionality affected

Saves ~2,100 lines of duplicate code while preserving all working functionality.

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

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

apps/web/src/app/games/page.tsx

@@ -18,14 +18,6 @@ function GamesPageContent() {
   // Get all players sorted by creation time
   const allPlayers = getAllPlayers().sort((a, b) => a.createdAt - b.createdAt)
 
-  const _handleGameClick = (gameType: string) => {
-    // Navigate directly to games using the centralized game mode with Next.js router
-    // Note: battle-arena has been removed - now handled by game registry as "matching"
-    console.log('🔄 GamesPage: Navigating with Next.js router (no page reload)')
-    if (gameType === 'memory-quiz') {
-      router.push('/games/memory-quiz')
-    }
-  }
 
   return (
     <div