feat(coupon): enhance theme compatibility by converting plan IDs to strings

app/Models/Coupon.php

@@ -23,4 +23,18 @@ class Coupon extends Model
             return PlanService::getPeriodKey($item);
         })->toArray();
     }
+
+    public function getLimitPlanIdsAttribute($value)
+    {
+        $planIds = json_decode($value, true);
+        
+        if (blank($planIds)) {
+            return null;
+        }
+        
+        return collect($planIds)
+            ->map(fn($id) => (string) $id)
+            ->values()
+            ->all();
+    }
 }