add core configuration

modules/common/common.nix

@@ -0,0 +1,47 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}: let
+  cfg = config.lily.common;
+in {
+  options.lily.common.enable = lib.mkEnableOption "activate common";
+  config = lib.mkIf cfg.enable {
+    programs.gnupg.agent = {
+      enable = true;
+      enableSSHSupport = true;
+    };
+    services.openssh.enable = true;
+    programs.zsh.enable = true;
+    environment.systemPackages = with pkgs; [
+      git
+      neovim
+      toybox
+      util-linux
+      tmux
+      ghostty
+
+      # encryption and filesystem
+      cryptsetup
+      age
+
+      # network tools
+      wget
+      curl
+      # FS-tools
+      unzip
+      gnutar
+      xz
+      bzip2
+      p7zip
+
+      netcat-gnu
+      dnsutils
+      fd
+      file
+      tree
+    ];
+    environment.shells = with pkgs; [zsh];
+  };
+}