26.05: source Lix from nixpkgs, fix disko btrfs label

nixos-26.05 removed lix_2_93, which the lix-module release-2.93 branch
hard-pins via lixFromNixpkgs (no 2.94 module release exists yet). Drop
the lix-module input and set nix.package = pkgs.lix, which is Lix 2.94.2
on 26.05 — so we stay on Lix, just sourced from nixpkgs.

Also: newer disko dropped the btrfs `label` option; pass -L nixos via
extraArgs instead so the impermanence rollback still finds the "nixos"
label.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

modules/profile/nanuqsaurus.nix

@@ -1,8 +1,11 @@
 { inputs }:
-{ ... }:
+{ pkgs, ... }:
 {
+  # Use Lix from nixpkgs (2.94.x on nixos-26.05). The lix-module's
+  # lixFromNixpkgs still pins lix_2_93, which nixos-26.05 removed.
+  nix.package = pkgs.lix;
+
   imports = [
-    inputs.lix-module.nixosModules.lixFromNixpkgs
     inputs.nix-index-database.nixosModules.nix-index
     inputs.nix-flatpak.nixosModules.nix-flatpak
     inputs.impermanence.nixosModules.impermanence

modules/system/disko-btrfs.nix

@@ -26,8 +26,9 @@
             size = "100%";
             content = {
               type = "btrfs";
-              extraArgs = [ "-f" ];
-              label = "nixos";
+              # Filesystem label "nixos" is required by the impermanence rollback
+              # logic. Newer disko dropped the `label` option; pass it to mkfs.btrfs.
+              extraArgs = [ "-f" "-L" "nixos" ];
               subvolumes = {
                 root = {
                   mountpoint = "/";