Implement/enforce `CHATROOM_MAX_MESSAGE_LEN`

[dotmacro]

Problem

Users can send/receive messages longer than CHATROOM_MAX_MESSAGE_LEN. (For reference, the largest message I tested was 262,144 plaintext chars.)

Nothing looks odd or broken. The app doesn't seem to lag. There's just a very long wall-of-text message to scroll past.

Solution

Fix.

[SebinSong]

I think this is a duplicate issue of https://github.com/okTurtles/group-income/issues/2217

[taoeffect]

yeah closing as duplicate