The seed import: clients with their matters, matched by name, idempotent (billing, admin)

The shape six-minute matter import reads. Clients are matched by exact name and matters by (client, name); missing rows are created, known rows are corrected in code, description, external_ref, billing, the record's own words, temporary, billable and active only where the seed differs, and an identical re-import changes nothing. One transaction: a refused row refuses the whole import.