Fix: Add proper top padding to prevent HeaderBar overlap on all main app pages

Match main app layout with proven working /competition route layout:
- Use px-6 py-6 pt-24 padding (same as /competition route)
- Ensures HeaderBar doesn't overlap content on /traders and /dashboard pages
- Provides consistent 6rem (96px) top clearance for fixed positioned HeaderBar
- Removes responsive padding variants that differed from competition page

This fixes header overlap issues across all main application routes.

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

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

web/src/App.tsx

@@ -298,7 +298,7 @@ function App() {
       />
 
       {/* Main Content */}
-      <main className="max-w-[1920px] mx-auto px-3 md:px-6 py-4 md:py-6">
+      <main className="max-w-[1920px] mx-auto px-6 py-6 pt-24">
         {currentPage === 'competition' ? (
           <CompetitionPage />
         ) : currentPage === 'traders' ? (