feat(hardening): declare hardening module using 'nix-mineral'

flake.nix

@@ -6,6 +6,10 @@
     nixos-hardware = {
       url = "github:NixOS/nixos-hardware/master";
     };
+    nix-mineral = {
+      url = "github:cynicsketch/nix-mineral";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
     disko = {
       url = "github:nix-community/disko/latest";
       inputs.nixpkgs.follows = "nixpkgs";