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/side-bar.html

@@ -85,13 +85,19 @@
             <button type="submit" class="catalog-filter-submit">Применить</button>
         </section>
 
+        {% if available_colors %}
         <section class="a-section color-section">
             <h2>Цвет</h2>
+            <select name="color" onchange="this.form.submit()">
+                <option value="">Любой</option>
+                {% for color in available_colors %}
+                    <option value="{{ color.id }}" {% if selected_color_id == color.id|stringformat:"i" %}selected{% endif %}>
+                        {{ color.name }}
+                    </option>
+                {% endfor %}
+            </select>
         </section>
-
-        <section class="a-section material-section">
-            <h2>Материал</h2>
-        </section>
+        {% endif %}
     </form>
 
     <section class="a-section promotions-section">