[FEATURE]: Add keybinds to scroll to prev/next user message #5029

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Add keybinds like messages_previous_user/messages_next_user to make it easier to scroll back through the user's view of the conversation. Similar functionality as /timeline, except when I do /timeline and press up/down I can't really see what I'm looking at, because it's very low contrast and the timeline popup is in the way. Adding messages_previous_user/messages_next_user would be a more "immediate" way to scroll back through my user messages, and see the model's response (without e.g. having to trigger and dismiss the timeline popup for every message).

I think this would subsume the new messages_last_user keybind, if I'm correctly reading the intent of the original request:

• [FEATURE]: add a command to scroll back to the user's last message #4847