Update to (somewhat?) dendritic pattern

Heavily inspired by https://github.com/Doc-Steve/dendritic-design-with-flake-parts.

> Atomic commits? Never heard of them!

modules/programs/cli-tools.nix

@@ -0,0 +1,9 @@
+{
+  flake.modules.nixos.cli-tools = { pkgs, ... }: {
+    environment.systemPackages = with pkgs; [
+      git
+      htop
+      vim
+    ];
+  };
+}