List conversations with filters and pagination
project_iduser_idsession_idstart_date, end_datepage (default 1)page_size (default 20, max 100)sort_by (started_at | last_activity_at | total_tasks | total_turns)sort_order (asc | desc)conversations[] items include:
id, project_id, user_id, session_idtotal_tasks, total_turnsstarted_at, last_activity_at