move systems into a separate directory

systems/common.nix

@@ -0,0 +1,59 @@
+{
+  pkgs,
+  nixpkgs,
+  ...
+}: {
+  environment.systemPackages = with pkgs; [
+    neovim
+    git
+    curl
+    nix-your-shell
+  ];
+
+  programs = {
+    fish = {
+      enable = true;
+      interactiveShellInit = ''
+        nix-your-shell fish | source
+      '';
+    };
+
+    direnv.enable = true;
+
+    command-not-found.enable = false;
+    nix-index = {
+      enable = true;
+      enableFishIntegration = true;
+    };
+  };
+
+  nixpkgs.config.allowUnfree = true;
+
+  nix = {
+    gc = {
+      automatic = true;
+      dates = "3d";
+      options = "-d";
+    };
+
+    settings = {
+      auto-optimise-store = true;
+      experimental-features = ["nix-command" "flakes"];
+    };
+  };
+
+  nix.registry = let
+    nixpkgsRegistry.flake = nixpkgs;
+  in {
+    nixpkgs = nixpkgsRegistry;
+    n = nixpkgsRegistry;
+  };
+
+  # This value determines the NixOS release from which the default
+  # settings for stateful data, like file locations and database versions
+  # on your system were taken. It‘s perfectly fine and recommended to leave
+  # this value at the release version of the first install of this system.
+  # Before changing this value read the documentation for this option
+  # (e.g. man configuration.nix or on https://nixos.org/nixos/options.html).
+  system.stateVersion = "23.11"; # Did you read the comment?
+}