major refactor

mod/common/nix.nix

@@ -0,0 +1,24 @@
+{
+  lib,
+  inputs,
+  config,
+  ...
+}:
+with lib;
+{
+  config = mkIf config.hd.common.nix.enable {
+    nix.settings = {
+      experimental-features = [
+        "nix-command"
+        "flakes"
+      ];
+      trusted-users = [ "root" ];
+      auto-optimise-store = true;
+    };
+    nix.registry = {
+      hd.flake = inputs.self;
+      nixpkgs.flake = inputs.nixpkgs;
+    };
+    nixpkgs.config.allowUnfree = false;
+  };
+}