fix: added the zod validation msg in the single player mode (#646)

packages/ui/primitives/document-flow/add-signature.types.tsx

@@ -1,7 +1,10 @@
 import { z } from 'zod';
 
 export const ZAddSignatureFormSchema = z.object({
-  email: z.string().min(1).email(),
+  email: z
+    .string()
+    .min(1, { message: 'Email is required' })
+    .email({ message: 'Invalid email address' }),
   name: z.string(),
   signature: z.string(),
 });