refactor: update module docstrings for clarity and consistency

backend/app/models/tenancy.py

@@ -1,7 +1,9 @@
+"""Shared tenancy-scoped model base classes."""
+
 from __future__ import annotations
 
 from app.models.base import QueryModel
 
 
 class TenantScoped(QueryModel, table=False):
-    pass
+    """Base class for models constrained to a tenant/organization scope."""