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/plugins/cmp/default.nix

@@ -0,0 +1,42 @@
+{ ... }: {
+  imports = [
+    ./keymaps.nix
+  ];
+
+  plugins = {
+    lspkind.enable = true;
+
+    cmp-nvim-lsp-signature-help.enable = true;
+
+    cmp = {
+      enable = true;
+      autoEnableSources = true;
+      autoLoad = true;
+
+      settings.sources = [
+        { name = "nvim_lsp"; }
+        { name = "nvim_lsp_signature_help"; }
+        { name = "path"; }
+      ];
+
+      settings.mapping = {
+        "<Tab>" = "cmp.mapping.select_next_item()";
+        "<S-Tab>" = "cmp.mapping.select_prev_item()";
+        "<C-Space>" = "cmp.mapping.complete()";
+        "<C-S-Space>" = "cmp.mapping.close()";
+        "<CR>" = "cmp.mapping.confirm({ behavior = cmp.ConfirmBehavior.Insert, select = true })";
+      };
+    };
+
+    lsp-format.enable = true;
+
+    none-ls = {
+      enable = true;
+      enableLspFormat = true;
+      sources.formatting = {
+        alejandra.enable = true;
+        nixpkgs_fmt.enable = true;
+      };
+    };
+  };
+}