flake: create common.nix for common options for all hosts

hosts/common.nix

@@ -0,0 +1,47 @@
+# This is for packages I want in all systems.
+# Keeping this list as small as possible is important,
+# since these also get installed to server,
+# which should have a small attack surface.
+{
+  self,
+  pkgs,
+  ...
+}: let
+  inherit (self.packages.${pkgs.stdenv.system}) helix fish;
+in {
+  environment.systemPackages = builtins.attrValues {
+    inherit
+      (pkgs)
+      cachix
+      calc
+      difftastic
+      eza
+      gcc
+      git
+      httpie
+      inetutils
+      jujutsu
+      just
+      lazygit
+      links2
+      linuxHeaders
+      neofetch
+      microfetch
+      nmap
+      polkit
+      ripgrep
+      smartmontools
+      trash-cli
+      util-linux
+      wireguard-tools
+      zip
+      zoxide
+      ;
+    inherit helix fish;
+  };
+  # helix as the only editor, a reasonable choice.
+  environment.sessionVariables.EDITOR = pkgs.lib.getExe' helix "hx";
+
+
+  
+}

hosts/default.nix

@@ -36,6 +36,7 @@ inputs: let
         (flatten (
           concatLists [
             (singleton ./${hostname}/default.nix)
+            (singleton ./common.nix)
             (
               filter (hasSuffix "module.nix") (
                 map toString (listFilesRecursive ../modules)