Adds topology CRUD to BaseRepository (NotImplementedError defaults) and
implements them in SQLModelRepository: create/get/list/delete topologies,
add/update/list LANs and TopologyDeckies, add/list edges, plus an atomic
update_topology_status that appends a TopologyStatusEvent in the same
transaction. Cascade delete sweeps children before the topology row.
Covered by tests/topology/test_repo.py (roundtrip, per-topology name
uniqueness, status event log, cascade delete, status filter) and an
extension to tests/test_base_repo.py for the NotImplementedError surface.
