Get Load Probe

Return per-status (and per-action) row counts for the calling client.

The query is two GROUP BY selects against api_requests:

1. Status totals across all rows belonging to the client (cheap; the table is partitioned by client in production and status is cardinality-bounded).
2. Status × action totals filtered to created_at >= now() - window (uses the existing (client, created_at) index).

Both queries are read-only and idempotent — safe to poll at 1 Hz.