Get usage statistics for the API key that authenticated this request.
Returns the same shape as the admin usage endpoint: lifetime totals,
calls this month/today, a 30-day daily series, distinct wallets tracked
this month, and the effective monthly quota (plan or per-key override).
Requires no special permission beyond valid auth (any DB-backed API key
can see its own usage). If the request wasn’t authenticated with a
database-backed API key (e.g. a JWT session, a partner key, or an
environment-based admin/client key — none of which have a per-key usage
record), returns 400.