docs: fix infinite scroll, update next.js, other fixes (#9441)

* update nextjs

* badge + scroll fixes

www/apps/ui/src/styles/globals.css

@@ -18,6 +18,14 @@
     @apply !bg-medusa-contrast-bg-highlight;
   }
 
+  * {
+    scrollbar-color: var(--docs-border-base) var(--docs-bg-base);
+  }
+
+  aside * {
+    scrollbar-color: var(--docs-border-base) var(--docs-bg-subtle);
+  }
+
   body {
     @apply text-ui-fg-subtle;
   }