feat: add favorites feature for users

- Implemented `Favorite` model with unique user-item constraint and timestamped records
- Added `favorites:index` and `favorites:toggle` views with AJAX support for toggling favorites
- Built templates and front-end assets for the favorites page and integration with item grids
- Extended header with favorites link and dynamic counter
- Added tests covering models, views, and templates for the favorites functionality
- Updated admin to enable management of favorites via Django admin interface

templates/catalog/_fragments/item-card.html

@@ -0,0 +1,57 @@
+<article class="item-card{% if item.id in favorite_item_ids %} is-favorite{% endif %}" data-item-card="{{ item.id }}">
+    <a class="item-card-media-link" href="{% url 'detail' item.category.slug item.slug %}" aria-label="Открыть товар {{ item.name }}">
+        {% with primary_image=item.primary_image %}
+            <div class="item-card-image">
+                {% if primary_image %}
+                    <img src="{{ primary_image.image.url }}" alt="{{ primary_image.alt|default:item.name }}">
+                {% else %}
+                    <div class="item-card-placeholder">Нет фото</div>
+                {% endif %}
+            </div>
+        {% endwith %}
+    </a>
+
+    <div class="item-card-body">
+        <div class="item-card-header">
+            <div class="item-card-category">
+                {{ item.category.name }}{% if item.subcategory %} / {{ item.subcategory.name }}{% endif %}
+            </div>
+            {% if request.user.is_authenticated %}
+                <form class="item-card-favorite-form" method="post" action="{% url 'favorites:toggle' %}" data-favorite-form>
+                    {% csrf_token %}
+                    <input type="hidden" name="item_id" value="{{ item.id }}">
+                    <input type="hidden" name="next" value="{{ request.get_full_path }}">
+                    <button
+                        class="item-card-favorite-button{% if item.id in favorite_item_ids %} is-active{% endif %}"
+                        type="submit"
+                        title="{% if item.id in favorite_item_ids %}Удалить из избранного{% else %}Добавить в избранное{% endif %}"
+                        aria-label="{% if item.id in favorite_item_ids %}Удалить из избранного{% else %}Добавить в избранное{% endif %}"
+                        data-favorite-button
+                        data-label-add="Добавить в избранное"
+                        data-label-remove="Удалить из избранного"
+                    >
+                        <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16" fill="currentColor" aria-hidden="true" focusable="false">
+                            <path d="m8 2.748-.717-.737C5.6.281 2.514.878 1.4 3.053c-.523 1.023-.641 2.5.314 4.385.92 1.815 2.834 3.989 6.286 6.357 3.452-2.368 5.365-4.542 6.286-6.357.955-1.886.838-3.362.314-4.385C13.486.878 10.4.28 8.717 2.01z"></path>
+                        </svg>
+                    </button>
+                </form>
+            {% else %}
+                <a class="item-card-favorite-button item-card-favorite-button--login" href="{% url 'users:login' %}?next={{ request.get_full_path|urlencode }}" title="Войдите, чтобы добавить в избранное" aria-label="Войдите, чтобы добавить в избранное" data-favorite-button data-label-add="Добавить в избранное" data-label-remove="Удалить из избранного">
+                    <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16" fill="currentColor" aria-hidden="true" focusable="false">
+                        <path d="m8 2.748-.717-.737C5.6.281 2.514.878 1.4 3.053c-.523 1.023-.641 2.5.314 4.385.92 1.815 2.834 3.989 6.286 6.357 3.452-2.368 5.365-4.542 6.286-6.357.955-1.886.838-3.362.314-4.385C13.486.878 10.4.28 8.717 2.01z"></path>
+                    </svg>
+                </a>
+            {% endif %}
+        </div>
+
+        <a class="item-card-title-link" href="{% url 'detail' item.category.slug item.slug %}" aria-label="Открыть товар {{ item.name }}">
+            <h2 class="item-card-title">{{ item.name }}</h2>
+        </a>
+        <div class="item-card-footer">
+            <span class="item-card-price">{{ item.price }} руб.</span>
+            <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>
+        </div>
+    </div>
+</article>