feat: Evotor + VK catalog sync, connections, and store/group filters

- Evotor catalog: background Celery task syncing stores/groups/products
  from Evotor API; UI pages with per-store and per-group sync toggles
- VK connection: manual token + group ID entry with inline test button
- Evotor connection: inline test button (calls /stores)
- VK catalog: background task syncing VK Market albums and products;
  separate catalog UI at /vk-catalog/albums
- SyncFilter extended to support entity_type=group with parent_entity_id
- Migration 0004: vk_cached_albums + vk_cached_products tables
- Beat schedule updated to run both refresh_catalog and refresh_vk_catalog
- README updated with new schema, routes, tasks, and config

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

web/templates/base.html

@@ -17,7 +17,8 @@
             <ul class="nav-links">
                 {% if user %}
                     <li><a href="/connections">Подключения</a></li>
-                    <li><a href="/catalog">Каталог</a></li>
+                    <li><a href="/catalog">Каталог Эвотор</a></li>
+                    <li><a href="/vk-catalog/albums">Каталог ВК</a></li>
                     <li><a href="/sync">Синхронизация</a></li>
                     {% if user.role in ('admin', 'system') %}
                     <li><a href="/admin/users"><i class="bi bi-shield-lock"></i> Админ</a></li>
@@ -34,7 +35,8 @@
                 <summary role="button" class="outline secondary icon-btn"><i class="bi bi-list"></i></summary>
                 <ul>
                     <li><a href="/connections">Подключения</a></li>
-                    <li><a href="/catalog">Каталог</a></li>
+                    <li><a href="/catalog">Каталог Эвотор</a></li>
+                    <li><a href="/vk-catalog/albums">Каталог ВК</a></li>
                     <li><a href="/sync">Синхронизация</a></li>
                     {% if user.role in ('admin', 'system') %}
                     <li><a href="/admin/users">Админ</a></li>