lmcp-api#304. Read-only, aggregates only: no machine id, no address.

The probe list of /admin/connectivity-geo stops at 500 rows ordered by machines, so the networks with few machines are lost and a sum over it is a floor. This is the same window and the same rows, grouped here and not capped. Per target (always the four of the contract):

• machines: distinct machines that reported the target; failing: those with at least one probe that did not end ok; ok = machines - failing.
• by_country, by_asn, by_stage: the FAILING machines of each group, most first. A machine that failed from two networks or at two stages counts once in each group, so a breakdown can add up to more than failing; failing is the total.

No small-group rule: like probe, a group of one machine is returned (finding the small networks is the point).