refactor(b3): dynamic entity registry, custom_fields permissions decoupled from contacts, write perms generated from registry

app/services/entity_permission_service.py

@@ -34,6 +34,7 @@ from app.models.contact_folder import ContactFolder
 from app.models.custom_field_definition import CustomFieldDefinition
 from app.models.entity_permission import EntityPermission
 from app.models.group import Group, UserGroup
+from app.models.notification import Notification
 from app.models.role import Role
 from app.models.saved_filter import SavedFilter
 from app.models.saved_view import SavedView
@@ -65,6 +66,7 @@ ENTITY_MODELS: dict[str, type] = {
     "saved_filter": SavedFilter,
     "saved_view": SavedView,
     "webhook": Webhook,
+    "notification": Notification,
     "custom_field_definition": CustomFieldDefinition,
     "contact_folder": ContactFolder,
 }