Fix SelectItem highlight not matching pill-shaped dropdown

Changed SelectItem border-radius from rounded-sm to rounded-xl to match
the pill-shaped aesthetic of SelectTrigger (rounded-full) and
SelectContent (rounded-2xl). The highlight now properly fills the item.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/components/ui/select.tsx

@@ -116,7 +116,7 @@ const SelectItem = React.forwardRef<
   <SelectPrimitive.Item
     ref={ref}
     className={cn(
-      "relative flex w-full cursor-default select-none items-center rounded-sm py-1.5 pl-8 pr-2 text-sm outline-none focus:bg-accent focus:text-accent-foreground data-[disabled]:pointer-events-none data-[disabled]:opacity-50",
+      "relative flex w-full cursor-default select-none items-center rounded-xl py-1.5 pl-8 pr-2 text-sm outline-none focus:bg-accent focus:text-accent-foreground data-[disabled]:pointer-events-none data-[disabled]:opacity-50",
       className
     )}
     {...props}