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/nixvim/_nixvim-config/default.nix

@@ -0,0 +1,19 @@
+{ ... }: {
+  imports = [
+    ./keymaps.nix
+    ./options.nix
+    ./plugins
+  ];
+
+  clipboard.register = "unnamedplus";
+
+  colorschemes.catppuccin = {
+    enable = true;
+    settings.flavour = "mocha";
+    settings.integrations = {
+      gitsigns = true;
+      treesitter = true;
+      cmp = true;
+    };
+  };
+}