List humanizations for one variant, sorted newest-first.
?variant_id= is required in this PR — org-wide unscoped listing
across projects ships in a later PR that adds a multi-table query
helper. The listed envelopes carry status + credit_cost + inputs but
not the per-strategy results array; fetch the individual
resource with GET /v1/humanizations/{id} to get the typed results.
Cost: read — rate bucket only.
Bearer authentication header of the form Bearer <token>, where <token> is your auth token.
1 <= x <= 200