List child API keys
Lists child API keys minted by the authenticated service key. Cross-service-key reads are NOT permitted: a service key only sees the keys it minted. Revoked rows are excluded from the list (use `GET /api/v1/keys/{id}` to read a specific revoked key).
Every successful read writes a `service_key_list_read` compliance event (audit-of-audit). Rate-limited to 600 requests per hour per service key.
