feat: enable color selection for cart items and enhance UI integration

- Added `selected_color` field to `CartItem` model with migration
- Updated color swatch behavior on product detail page with selection logic and disabled button handling
- Improved cart templates to display selected color alongside item details
- Modified `add_item_to_cart` service and `add` view to handle color selection
- Enhanced styles for active swatches and cart item color display

templates/orders/cart.html

@@ -34,6 +34,9 @@
 
                                     <div class="cart-item__info">
                                         <a class="cart-item__title" href="{% url 'detail' item.category.slug item.slug %}">{{ item.name }}</a>
+                                        {% if cart_item.selected_color %}
+                                            <span class="cart-item__color">({{ cart_item.selected_color.name }})</span>
+                                        {% endif %}
                                         <p class="cart-item__price">{{ item.price }} руб.</p>
 
                                         <div class="cart-item__controls">