feat(home): Pin <nixpkgs> to flake nixpkgs

modules/home/base/nix/default.nix

@@ -1,9 +1,17 @@
-{ pkgs, config, ... }:
 {
+  pkgs,
+  inputs,
+  config,
+  ...
+}: {
   config = {
     nix = {
       package = pkgs.lix;
 
+      # Pin system <nixpkgs> to flake nixpkgs version.
+      # i.e. for use in pkgs = import <nixpkgs> {}.
+      nixPath = ["nixpkgs=${inputs.nixpkgs}"];
+
       settings = {
         trusted-users = [
           "root"
@@ -40,7 +48,8 @@
 
     nixpkgs.config.import = "${config.xdg.configHome}/nixpkgs/config.nix";
 
-    xdg.configFile."nixpkgs/config.nix".text = # nix
+    xdg.configFile."nixpkgs/config.nix".text =
+      # nix
       ''
         {
           allowUnfree = true;