feat(shoukei): enable wluma ambient-light auto brightness

- read Asahi aop-sensors ALS via iio and drive eDP-1 backlight
- drop PrivateUsers for wluma so it can reach the real user D-Bus session
- remove hypridle 10min screen-dim listener: its brightnessctl writes fight
  wluma and get learned as manual adjustments

home/hosts/linux/12kingdoms-shoukei.nix

@@ -4,7 +4,10 @@ let
   mkSymlink = config.lib.file.mkOutOfStoreSymlink;
 in
 {
-  imports = [ ../../linux/gui.nix ];
+  imports = [
+    ../../linux/gui.nix
+    ./12kingdoms-shoukei/wluma.nix
+  ];
 
   programs.ssh.settings."github.com".IdentityFile = "${config.home.homeDirectory}/.ssh/${hostName}";
 

home/hosts/linux/12kingdoms-shoukei/wluma.nix

@@ -0,0 +1,43 @@
+{ ... }:
+# Automatic brightness for shoukei (the only host with an ambient light
+# sensor: aop-sensors-als, exposed through iio-sensor-proxy).
+#
+# wluma learns brightness preferences from manual adjustments (the QuickShell
+# slider counts as training data), then adjusts the backlight automatically
+# based on ambient light + screen contents.
+#
+# gamma = false keeps color temperature handled by noctalia's NightLight
+# (zwlr-gamma-control is an exclusive protocol, wluma and noctalia cannot
+# both own it). Other hosts keep the existing time-based NightLight setup.
+#
+# No extra udev rules or ACLs are needed: the sysfs brightness node is
+# root-owned, so wluma falls back to the systemd-logind D-Bus API
+# (org.freedesktop.login1.Session.SetBrightness), which authorizes active
+# sessions. Verified working inside Home Manager's default PrivateUsers
+# sandbox; do not "fix" it by disabling the sandbox.
+{
+  services.wluma = {
+    enable = true;
+    # Exactly one top-level ALS section is mandatory in wluma's config.
+    # The als.iio path scans /sys/bus/iio/devices and picks up the AOP
+    # ambient light sensor (aop-sensors-als) exported via iio-sensor-proxy.
+    settings.als.iio = {
+      path = "/sys/bus/iio/devices";
+      thresholds = {
+        "0" = "night";
+        "20" = "dark";
+        "80" = "dim";
+        "250" = "normal";
+        "500" = "bright";
+        "800" = "outdoors";
+      };
+    };
+    settings.output.backlight = [
+      {
+        name = "eDP-1";
+        path = "/sys/class/backlight/apple-panel-bl";
+        gamma = false;
+      }
+    ];
+  };
+}

home/linux/gui/base/hypridle/hypridle.conf

@@ -13,11 +13,11 @@ listener {
     on-resume = brightnessctl --restore --device=kbd_backlight         # turn on keyboard backlight.
 }
 
-listener {
+# NOTE: intentionally no 10min screen-dim listener here. Writing brightnessctl
-    timeout = 600                                # 10min.
+# directly fights the ambient-light auto-brightness daemon (wluma on shoukei):
-    on-timeout = brightnessctl -s set 10         # set monitor backlight to minimum, avoid 0 on OLED monitor.
+# wluma is adaptive, and hypridle's periodic brightness writes get learned as if
-    on-resume = brightnessctl -r                 # monitor backlight restore.
+# the user had made those adjustments. niri (26.04) has no built-in idle timers,
-}
+# so hypridle stays responsible for keyboard backlight, dpms and locking below.
 
 listener {
     timeout = 1200                                     # 20 minutes