feat: payment_method and referrals in cus expand

shared/models/cusModels/cusResModels/cusReferralsResponse.ts

@@ -0,0 +1,14 @@
+import z from "zod";
+
+export const CusReferralResponseSchema = z.object({
+  program_id: z.string(),
+  customer: z.object({
+    id: z.string(),
+    name: z.string().nullish(),
+    email: z.string().nullish(),
+  }),
+  reward_applied: z.boolean(),
+  created_at: z.number(),
+});
+
+export type CusReferralResponse = z.infer<typeof CusReferralResponseSchema>;