moved common out of systems

common/global/nix.nix

@@ -0,0 +1,28 @@
+{
+  inputs,
+  lib,
+  ...
+}: let
+  flakeInputs = lib.filterAttrs (_: lib.isType "flake") inputs;
+in {
+  nix = {
+    settings = {
+      trusted-users = [
+        "root"
+        "@wheel"
+      ];
+      auto-optimise-store = lib.mkDefault true;
+      experimental-features = [
+        "nix-command"
+        "flakes"
+        "ca-derivations"
+      ];
+      warn-dirty = false;
+      flake-registry = ""; # disable global flake registries
+    };
+
+    # Add each flake input as a registry and nix_path
+    registry = lib.mapAttrs (_: flake: {inherit flake;}) flakeInputs;
+    nixPath = lib.mapAttrsToList (n: _: "${n}=flake:${n}") flakeInputs;
+  };
+}