Get Contacts Known By

Batch known-by facts for a set of contacts: which org members know each contact, with source + first/last-touch timestamps. Facts only — no computed warmth score (explicit product decision, see the plan).

org_id-scoped like every other read here; a contact_id outside the caller's org simply yields no rows (contact_known_by carries its own org_id column, so no separate ownership check is needed).