consider default turning on mouse scrolling with tmux

I like to scroll in my tmux windows to see claude output. It's kind of awkward to do this from the keyboard (enter copy mode via ctrl-b then [ and then they work) since the arrows are remapped, but turning on mouse scrolling by default when you invoke tmux might be a good idea

`tmux new-session \; set-option -g mouse on`

Thanks for making this.

Scott

