refactor(variants): standardize variant structure and improve variant handling across components

src/app/shared/components/product-row-card/product-row-card.component.ts

@@ -37,7 +37,7 @@ export class ProductRowCardComponent {
   readonly addToCart = output<{ quantity: number; variant: unknown }>();
 
   protected readonly selectedVariantData = computed(() =>
-    this.variants().find((variant) => Object.is(variant.value, this.selectedVariant())),
+    this.variants().find((variant) => Object.is(variant.id, this.selectedVariant())),
   );
   protected readonly effectiveDescription = computed(
     () => this.selectedVariantData()?.descripcion ?? this.description(),