feat(cart): update CartItemResource to use visibleVariants method with included variant ID; enhance variant filtering logic

app/Domains/Cart/Resources/CartItemResource.php

@@ -38,7 +38,7 @@ class CartItemResource extends JsonResource
             'product' => $selectedItem === null ? null : [
                 'nombre' => $selectedItem->getName(),
                 'imagen' => $imageUrl,
-                'variants' => $this->catalogItem->variants
+                'variants' => $this->catalogItem->visibleVariants($this->variant_id)
                     ->map(fn (Variant $variant): array => [
                         'id' => $variant->id,
                         'precio' => $this->formatMoney($variant->getPrice()),

app/Domains/Catalog/Models/CatalogItem.php

@@ -172,10 +172,11 @@ class CatalogItem extends Model
     }
 
     /** @return Collection<int, Variant> */
-    public function visibleVariants(): Collection
+    public function visibleVariants(?int $includedVariantId = null): Collection
     {
         return $this->variants
-            ->filter(fn (Variant $variant): bool => $this->inventory_policy === InventoryPolicy::Unlimited
+            ->filter(fn (Variant $variant): bool => ($includedVariantId !== null && $variant->id === $includedVariantId)
+                || $this->inventory_policy === InventoryPolicy::Unlimited
                 || ($variant->inventory?->availableStock() ?? 0) > 0)
             ->values();
     }