Good question - but unfortunately you assessment is correct. We do not currently have a way (other than with the API Explorer) to via and/or send Chat messages via the Portal.
That said, we do have plans to implement a Chat Moderation portal. We're currently working on the scheduling of the work now - I expect it to start soon.
You'll find the item in our Roadmap here - https://portal.productboard.com/braincloud/1-braincloud-baas-roadmap/c/61-chat-moderation-portal?utm_medium=social&utm_source=portal_share
Feel free to add your +1 to it!