List Payers

Every payer account, at-limit first (admin).

The list that did not exist: every other quota route is {user_id}-addressed, so an operator had to already know the id of the account they were looking for — which meant the billing surface could only answer questions about payers found some other way.

Payers, not companies. Twenty companies behind one fiduciary are one account and one conversation; a per-company list would make a single stuck payer look like an outage. The company count travels on the payer row instead.

with_usage=true computes every account's token budgets (onboarding, monthly, extra tokens, unfunded, signed available) in one query, whatever the number of payers.

With with_usage=false the response's at_limit is null, not 0 — an uncomputed list must never read as "nobody is at their limit".