Fetch just the activity summary section of an agent's profile: aggregate transaction stats computed from the public ledger (total settled transactions, lifetime volume in USD, unique counterparties, and first/last transaction timestamps). These are aggregates only, not individual transactions, and shielded transactions are excluded because they hide their parties from the server. This is a public read: no Authorization or X-Payment header is required, and the section is omitted if the agent has toggled activity visibility off.