refactor(steam): configure SteamVR with Steam

configs/nixos/modules/desktop/apps/steam.nix

@@ -6,6 +6,9 @@
   ...
 }:
 # Steam game launcher and runtime integration.
+let
+  steamVrLauncher = "/home/${config.user.name}/.local/share/Steam/steamapps/common/SteamVR/bin/linux64/vrcompositor-launcher";
+in
 {
   options.modules.desktop.apps.steam.enable = lib.mkEnableOption "Steam game launcher";
 
@@ -21,7 +24,29 @@
 
     hardware.steam-hardware.enable = true;
 
-    programs.gamescope.enable = true;
+    programs.gamescope = {
+      enable = true;
+      capSysNice = true;
+    };
+
+    networking.firewall.allowedUDPPorts = [ 10400 ];
+
+    systemd.paths.steamvr-capabilities = {
+      wantedBy = [ "multi-user.target" ];
+      pathConfig = {
+        PathChanged = steamVrLauncher;
+        Unit = "steamvr-capabilities.service";
+      };
+    };
+
+    systemd.services.steamvr-capabilities = {
+      wantedBy = [ "multi-user.target" ];
+      path = [ pkgs.libcap ];
+      script = ''
+        setcap cap_sys_nice=eip ${lib.escapeShellArg steamVrLauncher}
+      '';
+      serviceConfig.Type = "oneshot";
+    };
 
     registry.window-icon.${config.networking.hostName}.steam = {
       class = "[Ss]team";