feat: implement validateRedirect utility for open redirect protection

app/utils/validateRedirect.ts

@@ -0,0 +1,9 @@
+export const validateRedirect = (redirect: string | unknown, fallback = '/dashboard'): string => {
+  if (typeof redirect !== 'string') {
+    return fallback;
+  }
+  if (redirect.startsWith('/') && !redirect.startsWith('//')) {
+    return redirect;
+  }
+  return fallback;
+}