Add Business tier and Paystack prepaid billing for POS.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/Models/Pos/ProSubscription.php

@@ -14,10 +14,14 @@ class ProSubscription extends Model
 
     public const STATUS_PAST_DUE = 'past_due';
 
+    public const PLAN_PRO = 'pro';
+
+    public const PLAN_ENTERPRISE = 'enterprise';
+
     protected $table = 'pos_pro_subscriptions';
 
     protected $fillable = [
-        'user_id', 'status', 'price_minor', 'currency', 'auto_renew',
+        'user_id', 'status', 'plan', 'price_minor', 'currency', 'auto_renew',
         'started_at', 'current_period_end', 'last_charged_at', 'canceled_at',
         'last_reference', 'last_error',
     ];