feat: VK OAuth flow, catalog sync improvements, and expanded test suite

- Add VK OAuth implicit flow: /vk-auth redirect, /vk-callback JS page,
  /vk-callback/save endpoint with state validation
- Add VK_CLIENT_ID/VK_CLIENT_SECRET to config
- Add refresh_token/token_expires_at columns to vk_connections (migration 0006)
- Fix vk_catalog task: handle price/thumb_photo as string or dict (VK API v5.199)
- Fix connections/vk/test: use groups.getById instead of market.getAlbums
  (works with both user and group tokens)
- Add orphan deletion to mirror_to_vk: VK products not in Evotor are removed
- Handle ungrouped Evotor products: push to "Без категории" VK album
- Respect SyncConfig.is_enabled in mirror_to_vk
- Add product count column to catalog groups page
- Add group name column to catalog products page
- Expand test suite: 73 new tests covering connections routes, catalog routes,
  vk_sync task logic, and catalog task helpers (138 total, all passing)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/templates/catalog/groups.html

@@ -23,6 +23,7 @@
                 <tr>
                     <th>Синхронизация</th>
                     <th>Название</th>
+                    <th>Количество товаров</th>
                     <th>ID</th>
                     <th>Обновлено</th>
                     <th></th>
@@ -47,6 +48,7 @@
                         </form>
                     </td>
                     <td><i class="bi bi-folder2 me-1 text-muted"></i> <strong>{{ g.name }}</strong></td>
+                    <td class="text-muted small">{{ product_counts.get(g.evotor_id, 0) }}</td>
                     <td class="text-muted small">{{ g.evotor_id }}</td>
                     <td class="text-muted small">{{ g.fetched_at | datefmt }}</td>
                     <td>

web/templates/catalog/products.html

@@ -40,6 +40,7 @@
             <thead>
                 <tr>
                     <th>Название</th>
+                    <th>Группа</th>
                     <th>Артикул</th>
                     <th>Цена</th>
                     <th>Остаток</th>
@@ -52,6 +53,7 @@
                 {% for p in products %}
                 <tr>
                     <td>{{ p.name }}</td>
+                    <td class="text-muted small">{{ group_map.get(p.group_evotor_id) or '—' }}</td>
                     <td class="text-muted small">{{ p.article_number or '—' }}</td>
                     <td>{% if p.price is not none %}{{ p.price | price }}{% else %}—{% endif %}</td>
                     <td>{% if p.quantity is not none %}{{ p.quantity }}{% else %}—{% endif %}</td>

web/templates/connections.html

@@ -134,14 +134,15 @@
             {% endif %}
 
             <div class="card-body">
-                <details {% if not vk %}open{% endif %}>
-                    <summary>
-                        {% if vk %}Обновить подключение{% else %}Подключить ВКонтакте{% endif %}
-                    </summary>
-                    <p class="text-muted small mt-2">
-                        Укажите токен пользователя VK с правами <code>market,photos,groups</code>
-                        и ID сообщества, в котором включён Маркет.
-                    </p>
+                <div class="mt-3">
+                    <a href="/vk-auth" role="button">
+                        <i class="bi bi-box-arrow-in-right me-1"></i>
+                        {% if vk %}Переподключить ВКонтакте{% else %}Войти через ВКонтакте{% endif %}
+                    </a>
+                </div>
+
+                <details class="mt-3">
+                    <summary class="text-muted small">Ввести токен вручную</summary>
                     <form method="post" action="/connections/vk" class="mt-2">
                         <label>
                             Токен доступа VK