CUB-116: Scaffold React frontend — Vite, TS, Tailwind

frontend/src/components/ErrorState.tsx

@@ -0,0 +1,21 @@
+export default function ErrorState({
+  message = 'Something went wrong.',
+  onRetry,
+}: {
+  message?: string
+  onRetry?: () => void
+}) {
+  return (
+    <div className="flex min-h-[120px] flex-col items-center justify-center gap-3 rounded-xl border border-red-500/20 bg-red-950/30 p-6 text-center">
+      <p className="text-sm text-red-300">{message}</p>
+      {onRetry && (
+        <button
+          onClick={onRetry}
+          className="rounded-lg bg-red-600 px-3 py-1.5 text-xs font-medium text-white hover:bg-red-700"
+        >
+          Retry
+        </button>
+      )}
+    </div>
+  )
+}