fix: resolve ESLint errors in Button and Skeleton components

- Button: suppress react-refresh/only-export-components for buttonVariants re-export
- Skeleton: replace empty interface with type alias, replace Math.random() with static widths array

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/ui/Button.tsx

@@ -60,4 +60,5 @@ export function Button({
   )
 }
 
+// eslint-disable-next-line react-refresh/only-export-components
 export { buttonVariants }

frontend/src/components/ui/Skeleton.tsx

@@ -1,6 +1,6 @@
 import { cn } from '@/lib/utils'
 
-interface SkeletonProps extends React.HTMLAttributes<HTMLDivElement> {}
+type SkeletonProps = React.HTMLAttributes<HTMLDivElement>
 
 export function Skeleton({ className, ...props }: SkeletonProps) {
   return (
@@ -27,6 +27,8 @@ export function CardSkeleton({ className }: { className?: string }) {
   )
 }
 
+const COL_WIDTHS = ['35%', '45%', '25%', '40%', '30%', '50%']
+
 export function TableRowSkeleton({ cols = 4 }: { cols?: number }) {
   return (
     <div className="flex items-center gap-4 px-4 py-3">
@@ -34,7 +36,7 @@ export function TableRowSkeleton({ cols = 4 }: { cols?: number }) {
         <Skeleton
           key={i}
           className="h-4"
-          style={{ width: `${20 + Math.random() * 30}%` }}
+          style={{ width: COL_WIDTHS[i % COL_WIDTHS.length] }}
         />
       ))}
     </div>