feat: implement product attribute selector component and integrate into product detail page

src/app/features/store/pages/product-detail-page/product-detail-page.component.html

@@ -69,6 +69,7 @@
                     type="button"
                     class="product-detail__quantity-button"
                     aria-label="Aumentar cantidad"
+                    [disabled]="quantity() >= (selectedVariant()?.stock ?? 1)"
                     (click)="increaseQuantity()"
                   >
                     +
@@ -80,11 +81,12 @@
                     class="product-detail__cta"
                     variant="secondary"
                     type="button"
+                    [disabled]="!selectedVariant()"
                   >
                     Agregar al carrito
                   </app-button>
 
-                  <app-button class="product-detail__cta" type="button">
+                  <app-button class="product-detail__cta" type="button" [disabled]="!selectedVariant()">
                     Comprar
                   </app-button>
                 </div>

src/app/features/store/pages/product-detail-page/product-detail-page.component.ts

@@ -154,10 +154,14 @@ export class ProductDetailPageComponent implements OnInit, OnDestroy {
 
   protected onVariantChange(variant: ProductVariantMap | null): void {
     this.selectedVariant.set(variant);
+    if (variant && this.quantity() > variant.stock) {
+      this.quantity.set(Math.max(1, variant.stock));
+    }
   }
 
   protected increaseQuantity(): void {
-    this.quantity.update((current) => current + 1);
+    const currentStock = this.selectedVariant()?.stock ?? 1;
+    this.quantity.update((current) => current < currentStock ? current + 1 : current);
   }
 
   protected decreaseQuantity(): void {