feat: implement product and variant CRUD management service with attachment handling

app/Domains/Catalog/Services/ProductService.php

@@ -10,6 +10,7 @@ use App\Domains\Tenant\Models\Tenant;
 use Illuminate\Contracts\Pagination\LengthAwarePaginator;
 use Illuminate\Http\UploadedFile;
 use Illuminate\Support\Facades\DB;
+use Illuminate\Validation\ValidationException;
 use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
 
 class ProductService
@@ -332,6 +333,12 @@ class ProductService
             throw new NotFoundHttpException('Product variant not found for product.');
         }
 
+        if ($variantId !== null && $selectedVariant->stock <= 0) {
+            throw ValidationException::withMessages([
+                'variant_id' => 'La variante seleccionada no tiene stock.',
+            ]);
+        }
+
         $selectedVariant ??= $product->variants->first();
 
         if ($selectedVariant !== null) {