🐞 Stop serving former clients as active API clients

[JFWooten4]

The API currently continues to serve data for old/former clients alongside current clients.

Historical records may still need to remain available internally, and some historical information may appropriately remain public, but the API should not represent a former client as though they are still an active BlockTransfer client.

This should be handled at the WK-toml layer so older clients of the API do not have to independently infer whether an issuer is still active.