feat: add pagination and color filter to catalog view and templates

- Implemented pagination for catalog items with Django's Paginator
- Updated `item-list.html` to include pagination controls
- Added color filtering logic to catalog view with support for `Color` model
- Enhanced `side-bar.html` with a dynamic color dropdown filter
- Adjusted filtering URL logic to accommodate color filters and pagination parameters
- Prefetched `colors` in item queries to optimize performance

templates/catalog/_fragments/item-list.html

@@ -1,3 +1,18 @@
 <main class="item-list">
-    {% include "_fragments/item-grid.html" with items=items empty_message="В этой категории пока нет товаров." %}
+    {% include "_fragments/item-grid.html" with items=page_obj empty_message="В этой категории пока нет товаров." %}
+
+    {% if paginator.num_pages > 1 %}
+    <nav class="catalog-pagination">
+        {% if page_obj.has_previous %}
+            <a href="?{{ pagination_query_string }}&page={{ page_obj.previous_page_number }}" class="catalog-pagination__btn">&laquo;</a>
+        {% endif %}
+        {% for i in paginator.page_range %}
+            <a href="?{{ pagination_query_string }}&page={{ i }}"
+               class="catalog-pagination__btn {% if i == page_obj.number %}active{% endif %}">{{ i }}</a>
+        {% endfor %}
+        {% if page_obj.has_next %}
+            <a href="?{{ pagination_query_string }}&page={{ page_obj.next_page_number }}" class="catalog-pagination__btn">&raquo;</a>
+        {% endif %}
+    </nav>
+    {% endif %}
 </main>