feat(ymir): add light for managing backlight.

hosts/ymir/configuration.nix

@@ -101,6 +101,9 @@
     binfmt = true;
   };
 
+  # Enable light for image control
+  programs.light.enable = true;
+
   # Define a user account. Don't forget to set a password with ‘passwd’.
   users.users.crony = {
     isNormalUser = true;