Turn off keyboard backlighting when idle

Closes #3319
Co-authored-by: @pukljak

config/hypr/hypridle.conf

@@ -15,6 +15,12 @@ listener {
     on-timeout = loginctl lock-session # lock screen when timeout has passed
 }
 
+listener {
+    timeout = 330                                            # 5.5min
+    on-timeout = brightnessctl -sd '*::kbd_backlight' set 0  # save state and turn off keyboard backlight
+    on-resume = brightnessctl -rd '*::kbd_backlight'         # restore keyboard backlight
+}
+
 listener {
     timeout = 330                                            # 5.5min
     on-timeout = hyprctl dispatch dpms off                   # screen off when timeout has passed