feat: add referral_code

app/Models/User.php

@@ -20,9 +20,16 @@ class User extends Authenticatable
         'male' => 1,
         'female' => 2,
     ];
+
+    // Referral program (کد معرف): successful invites needed for a free month,
+    // and the app whose monthly product is granted as the reward.
+    const REFERRAL_SUBSCRIPTION_TARGET = 10;
+    const REFERRAL_PACKAGE_NAME = 'com.approagency.meditation';
+
     protected $guarded = [];
     protected $casts = [
     'mobile_verified_at' => 'datetime',
+    'referral_subscription_granted_at' => 'datetime',
 ];
     protected $hidden = [
         'password',