feat: per-task on/off switches on /sync page for staged rollout

Adds evo_mirror_enabled and vk_mirror_enabled flags to SyncConfig.
Each of the three background tasks (Зеркало Эвотор / Зеркало ВК /
Синхронизация) can now be enabled independently from the /sync page.

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

web/tasks/vk_catalog.py

@@ -10,7 +10,7 @@ from celery import shared_task
 import web.lib.api_logger as api_logger
 from web.config import settings
 from web.database import SessionLocal
-from web.models.connections import VkCachedAlbum, VkCachedProduct, VkConnection
+from web.models.connections import SyncConfig, VkCachedAlbum, VkCachedProduct, VkConnection
 
 logger = logging.getLogger(__name__)
 
@@ -172,6 +172,9 @@ def refresh_vk_catalog(self) -> dict:
             .all()
         )
         for conn in connections:
+            cfg = db.query(SyncConfig).filter_by(user_id=conn.user_id).first()
+            if not cfg or not cfg.vk_mirror_enabled:
+                continue
             try:
                 _sync_user(db, conn.user_id, conn.access_token, conn.vk_user_id)
                 results["ok"] += 1