feat: add color, discount price, and new item attributes to catalog and update UI

- Introduced `Color` model with admin and added a color field to items
- Added `discount_price` and `is_new` fields to the `Item` model with necessary migrations
- Updated pricing logic to display original and discount prices in templates
- Enhanced product detail and item card templates with color swatches and metadata
- Added sidebar sections for sales and new items with paginated mini-cards
- Updated styles to support discount pricing, swatches, and sidebar mini-cards
- Extended catalog views to filter by sales or new items and updated filtering logic

templates/catalog/_fragments/item-card.html

@@ -48,7 +48,14 @@
             <h2 class="item-card-title">{{ item.name }}</h2>
         </a>
         <div class="item-card-footer">
-            <span class="item-card-price">{{ item.price }} руб.</span>
+            <div class="item-card-price-block">
+                <span class="item-card-price{% if item.has_discount %} item-card-price--discount{% endif %}">
+                    {{ item.display_price }} руб.
+                </span>
+                {% if item.has_discount %}
+                    <span class="item-card-price-original">{{ item.price }} руб.</span>
+                {% endif %}
+            </div>
             <span class="item-card-availability {% if item.is_available %}available{% else %}unavailable{% endif %}">
                 {% if item.is_available %}В наличии{% else %}Нет в наличии{% endif %}
             </span>