backlight: use brightnessctl instead of removed light binary

nixpkgs 26.05 dropped the 'light' package. Switch BacklightService to brightnessctl and bundle it in the wrapper PATH. Bump flake nixpkgs to nixos-26.05.

flake.lock

@@ -17,16 +17,16 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1776169885,
-        "narHash": "sha256-l/iNYDZ4bGOAFQY2q8y5OAfBBtrDAaPuRQqWaFHVRXM=",
+        "lastModified": 1780902259,
+        "narHash": "sha256-q8yYEC5f1mFlQO9RGna4LTc9QrcvWunX6FYp83munkQ=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "4bd9165a9165d7b5e33ae57f3eecbcb28fb231c9",
+        "rev": "bd0ff2d3eac24699c3664d5966b9ef36f388e2ca",
         "type": "github"
       },
       "original": {
         "owner": "NixOS",
-        "ref": "nixos-unstable",
+        "ref": "nixos-26.05",
         "repo": "nixpkgs",
         "type": "github"
       }

flake.nix

@@ -2,7 +2,7 @@
   description = "nova-shell - minimal Quickshell bar for niri";
 
   inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-26.05";
 
     quickshell = {
       url = "git+https://git.outfoxxed.me/outfoxxed/quickshell";

nix/package.nix

@@ -8,6 +8,7 @@
   nova-shaders,
   nova-plugin,
   glib,
+  brightnessctl,
 }:
 let
   shellSrc = lib.cleanSourceWith {
@@ -53,6 +54,7 @@ symlinkJoin {
         lib.makeBinPath [
           nova-stats
           glib
+          brightnessctl
         ]
       }
   '';

shell/services/BacklightService.qml

@@ -14,12 +14,12 @@ QtObject {
 
     function adjust(delta) {
         const step = NS.ModulesService.backlightStep || 5;
-        _adjProc.cmd = delta > 0 ? "light -A " + step : "light -U " + step;
+        _adjProc.cmd = delta > 0 ? "brightnessctl set " + step + "%+" : "brightnessctl set " + step + "%-";
         _adjProc.running = true;
     }
 
     function setPercent(pct) {
-        _adjProc.cmd = "light -S " + Math.round(Math.max(0, Math.min(100, pct)));
+        _adjProc.cmd = "brightnessctl set " + Math.round(Math.max(0, Math.min(100, pct))) + "%";
         _adjProc.running = true;
     }