open https://gitlab.synchro.net/main/sbbs/-/issues/511

If the auto message was a message base (i.e. display only the latest message), it'd enable:
- deleting the current message would auto revert to the previous (non-deleted) message
- meta data stored in (and displayed from) message header rather than part of the message
- allow voting, replying, quoting (traditional message base functions)
- full message authoring tools (message editors)

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