[idea] Option to preserve scrollback on clear

[saurabh-hirani]

idea / problem

clear and Ctrl+L erase the scrollback buffer in herdr. In tmux, the same commands clear the visible screen but scrollback remains - you can scroll up to see previous output. On macOS, clear -x (which should skip scrollback erase) sends the same CSI 3 J sequence as clear, so it's not a workaround.

requested change

A config option (e.g. suppress_erase_scrollback = true under [advanced]) that makes herdr ignore CSI 3 J and only process CSI 2 J. This would let clear behave like it does in tmux - clearing the screen without losing history.

why you want this

Scrollback is how I reference previous command output during a session. Losing it on every clear means I have to re-run commands or pipe to files. Every tmux user migrating to herdr will hit this.