Ranks the READER axis by tenant: which tenants' principals performed the most audit reads within the period.

This does NOT answer "whose audit trail was read". That is the subject axis, and it has its own operation — getTopSubjectTenants. The two read alike and mean opposite things, which is why they are separate operations with separate labels rather than one operation with an axis parameter: a value a caller can omit must never decide which of two questions a ranking answered.

The operationId and the ranking itself are unchanged — only the label is. The defect was the label.