refactor: add notifications module

surfsense_backend/app/notifications/__init__.py

@@ -0,0 +1,15 @@
+"""User notifications: persistence, service, and HTTP API.
+
+Emit notifications via :class:`~app.notifications.service.NotificationService`;
+the router in :mod:`app.notifications.api` exposes the inbox endpoints.
+"""
+
+from __future__ import annotations
+
+from app.notifications.persistence import Notification
+from app.notifications.service import NotificationService
+
+__all__ = [
+    "Notification",
+    "NotificationService",
+]