feat(homepage): significantly increase mobile hero abacus size

Increased mobile scale from 2.5 to 3.5 to better utilize available screen
space on mobile devices. Screenshot review showed ample room above and
below the abacus without risk of overlapping title or scroll hint.

Final scales:
- Mobile (base): scale(3.5) - 75% larger than original
- Medium (md): scale(3.5) - 16% larger than original
- Desktop (lg): scale(4.25) - 6% larger than original

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

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

apps/web/src/components/HeroAbacus.tsx

@@ -131,7 +131,7 @@ export function HeroAbacus() {
       >
         <div
           className={css({
-            transform: { base: 'scale(2.5)', md: 'scale(3.5)', lg: 'scale(4.25)' },
+            transform: { base: 'scale(3.5)', md: 'scale(3.5)', lg: 'scale(4.25)' },
             transformOrigin: 'center center',
             transition: 'all 0.5s cubic-bezier(0.4, 0, 0.2, 1)',
           })}