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/tasks/celery_app.py

@@ -1,4 +1,5 @@
 from celery import Celery
+from celery.schedules import timedelta
 
 from web.config import settings
 
@@ -20,4 +21,17 @@ celery_app.conf.update(
         "web.tasks.catalog.*": {"queue": "default"},
         "web.notifications.tasks.*": {"queue": "notifications"},
     },
+    beat_schedule={
+        "refresh-catalog": {
+            "task": "web.tasks.catalog.refresh_catalog",
+            "schedule": timedelta(seconds=settings.CATALOG_REFRESH_INTERVAL_SECONDS),
+        },
+        "refresh-vk-catalog": {
+            "task": "web.tasks.vk_catalog.refresh_vk_catalog",
+            "schedule": timedelta(seconds=settings.CATALOG_REFRESH_INTERVAL_SECONDS),
+        },
+    },
 )
+
+# Register task modules so beat/worker can discover them
+celery_app.autodiscover_tasks(["web.tasks.catalog", "web.tasks.vk_catalog"])