feat(backend): migrate auth and notifications off email

apps/notifications/tasks.py

@@ -0,0 +1,14 @@
+import logging
+
+from celery import shared_task
+
+from apps.notifications.services import RedisNotificationStore
+
+logger = logging.getLogger(__name__)
+
+
+@shared_task
+def cleanup_notification_retention():
+    removed = RedisNotificationStore.cleanup_expired()
+    logger.info("Cleaned up %s expired notifications", removed)
+    return removed