macbook: add keyboard backlight key bindings and permissions

- Add XF86KbdBrightnessUp/Down keybindings (Macbook-only) using swayosd
  for consistent OSD behaviour with screen brightness and volume
- Enable hardware.acpilight for udev rules allowing video group to write
  to /sys/class/leds/ (keyboard backlight)
- Add fred to the video group so brightnessctl/swayosd can write backlight values

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

hosts/FredOS-Macbook.nix

@@ -24,6 +24,10 @@
     boot.loader.systemd-boot.configurationLimit = 5;
     boot.initrd.systemd.enable = true;
 
+    # Allow video group (fred) to write to /sys/class/backlight and /sys/class/leds
+    # (screen brightness and keyboard backlight)
+    hardware.acpilight.enable = true;
+
     services.logind.settings.Login = {
       HandleLidSwitch = "suspend";
       HandleLidSwitchExternalPower = "suspend";

settings/hyprland.nix

@@ -312,6 +312,9 @@ in
             ", XF86AudioMute,        exec, swayosd-client --output-volume mute-toggle"
             ", XF86MonBrightnessUp,   exec, swayosd-client --brightness raise"
             ", XF86MonBrightnessDown, exec, swayosd-client --brightness lower"
+          ] ++ lib.optionals isMacbook [
+            ", XF86KbdBrightnessUp,   exec, swayosd-client --keyboard-brightness raise"
+            ", XF86KbdBrightnessDown, exec, swayosd-client --keyboard-brightness lower"
           ];
 
           bindl = [

settings/users.nix

@@ -11,7 +11,7 @@
 	users.users.fred = {
 		isNormalUser = true;
 		description = "fred";
-		extraGroups = [ "networkmanager" "wheel" "docker" ];
+		extraGroups = [ "networkmanager" "wheel" "docker" "video" ];
 		packages = lib.optionals
 			(lib.elem config.networking.hostName [ "FredOS-Gaming" "FredOS-Macbook" ])
 			(with pkgs; [ bazaar ]);