[FEATURE]: Scroll line-by-line like Vim ctrl-e and ctrl-y

[NathanFlurry]

Feature hasn't been suggested before.

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

Describe the enhancement you want to request

Vim provides ctrl-e and ctrl-y scroll line-by-line behavior. Would be nice for OpenCode to support this.

Biggest motivation here is that OpenCode does not play nice with tmux scrollback, so all of the scroll keybindings that vim users are used to need to be replicated.