Set brightness without having to install another CLI program

[sloganking]

Currently before the assistant can set the brightness, the user has to cargo install luster. As the set_screen_brightness() function just calls luster as a CLI command to set the brightness.

fn set_screen_brightness(brightness: u32) -> Option<()> {
    if brightness > 100 {
        println!("Brightness must be between 0 and 100");
        return None;
    }

    Command::new("luster")
        .arg(brightness.to_string())
        .output()
        .ok()
        .map(|_| ())
}

This is annoying and it would be more convenient if brightness setting came when the assistant is installed, with no other steps.