pub fn split_window_horizontal(
target_pane: &str,
size_pct: u32,
) -> Result<String>Expand description
Helper: run tmux set -t <session> <option> <value>.
Split a pane horizontally (creates a new pane to the right).
target_pane is a tmux pane ID (e.g., %0). Returns the new pane’s ID.