Optimize scroll performance

- Cache isMobile check in edge swipe detection to avoid layout thrashing
- Remove scroll-behavior: smooth from tab slider
- Remove -webkit-overflow-scrolling: touch

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/styles/Layout.css

@@ -96,10 +96,8 @@ label,
   max-width: 100%;
   overflow-x: auto;
   overflow-y: hidden;
-  -webkit-overflow-scrolling: touch;
   scrollbar-width: none;
   -ms-overflow-style: none;
-  scroll-behavior: smooth;
 }
 
 .page-tabs-slider::-webkit-scrollbar,