feat: add CopycatWarningToast component for user warnings (#12733)

Introduced a new CopycatWarningToast component that displays a warning about copycat sites. The toast appears at the top-center of the screen and can be dismissed, with the dismissal state stored in local storage to prevent reappearing. Integrated the component into the RootLayout for global visibility.

frontend/src/components/copycat-warning-toast.tsx

@@ -0,0 +1,24 @@
+"use client";
+
+import { useEffect } from "react";
+import { toast } from "sonner";
+
+const STORAGE_KEY = "copycat-warning-dismissed";
+
+export function CopycatWarningToast() {
+  useEffect(() => {
+    if (typeof window === "undefined")
+      return;
+    if (localStorage.getItem(STORAGE_KEY) === "true")
+      return;
+
+    toast.warning("Beware of copycat sites. Always verify the URL is correct before trusting or running scripts.", {
+      position: "top-center",
+      duration: Number.POSITIVE_INFINITY,
+      closeButton: true,
+      onDismiss: () => localStorage.setItem(STORAGE_KEY, "true"),
+    });
+  }, []);
+
+  return null;
+}