fix(website): make back-to-top scroll instant instead of smooth

The smooth scroll behavior felt sluggish on a 505-row page. Instant
jump is more responsive for a utility button.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

website/static/main.js

@@ -294,7 +294,7 @@ if (backToTop) {
     }
   });
   backToTop.addEventListener('click', function () {
-    window.scrollTo({ top: 0, behavior: 'smooth' });
+    window.scrollTo({ top: 0 });
   });
 }