We need a way to list 1:1 chats and ad-hoc group rooms the token owner can see in the app. Team rooms already work. Personal chats and non-Team rooms do not. GET /conversations/:id works if we already have the ID, but there is no discovery path. A mailbox filter or endpoint for chats (distinct from email) would fix it. Guest conversations returning only id and last_activity_at is also too thin for an assistant that needs to work those rooms.