feat(notifications): add redis-backed sse notification streaming

apps/notifications/tasks.py

@@ -0,0 +1,11 @@
+from celery import shared_task
+from django.conf import settings
+
+from apps.notifications.services import RedisNotificationStore
+
+
+@shared_task(name="notifications.cleanup_redis_notifications")
+def cleanup_redis_notifications():
+    return RedisNotificationStore.cleanup_expired(
+        retention_days=settings.NOTIFICATION_RETENTION_DAYS
+    )