fix(homepage): reduce mobile abacus scale to prevent scroll hint overlap

Reduced mobile scale from 2.8 to 2.5 to ensure the "Scroll to explore"
hint at the bottom is not covered by the abacus.

Final scales:
- Mobile (base): scale(2.5) - 25% larger than original, no overlap
- 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(2.8)', md: 'scale(3.5)', lg: 'scale(4.25)' },
+            transform: { base: 'scale(2.5)', md: 'scale(3.5)', lg: 'scale(4.25)' },
             transformOrigin: 'center center',
             transition: 'all 0.5s cubic-bezier(0.4, 0, 0.2, 1)',
           })}