fix: disable cancel button when there is no window history

apps/web/src/app/(signing)/sign/[token]/form.tsx

@@ -120,6 +120,7 @@ export const SigningForm = ({ document, recipient, fields }: SigningFormProps) =
                 className="dark:bg-muted dark:hover:bg-muted/80 w-full  bg-black/5 hover:bg-black/10"
                 variant="secondary"
                 size="lg"
+                disabled={typeof window !== 'undefined' && window.history.length <= 1}
                 onClick={() => router.back()}
               >
                 Cancel