refactor(catalog): Complete catalog refactor to simplify its data model and its querying.

source commits: refactor/catalog

app/Domains/Purchase/Models/Purchase.php

@@ -119,7 +119,7 @@ class Purchase extends Model
 
         $cart = $this->relationLoaded('cart')
             ? $this->getRelation('cart')
-            : $this->cart()->with('items.buyable')->first();
+            : $this->cart()->with(['items.catalogItem', 'items.variant'])->first();
 
         if (! $cart) {
             return 0.0;