Use Home Manager as a NixOS module

Replace the standalone homeConfigurations output with the Home Manager
NixOS module, so a single nixos-rebuild applies both the system and the
user configuration.

- flake.nix: import home-manager.nixosModules.home-manager, set
  home-manager.users.leo, drop the now-unused pkgs let-binding
  (allowUnfree comes from configuration.nix via useGlobalPkgs)
- home.nix: drop home.username/homeDirectory and
  programs.home-manager.enable, all provided by the module
- README.md: remove the separate install and home-manager switch steps

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FStCxmGBXQUWjgN2xMSvjU

README.md

@@ -6,6 +6,8 @@
 4. Add flakes support by appending `nix.settings.experimental-features = ["nix-command" "flakes"];`
 5. Rebuild `nixos-rebuild switch`
 6. Clone this repo to your destination of choice (I go with ~/.dotfiles for the time being)
-7. Install [home-manager](https://nix-community.github.io/home-manager/)
-8. Switch to the current version `nixos-rebuild switch --flake . --impure` (Impure, because we do not provide hardware configuration, since it is machine dependant)
-9. Switch to the current version of home-manager `home-manager switch --flake .`
+7. Switch to the current version `nixos-rebuild switch --flake . --impure` (Impure, because we do not provide hardware configuration, since it is machine dependant)
+
+Home Manager is included as a NixOS module, so `nixos-rebuild` applies both the
+system and the user configuration. There is no separate `home-manager switch`
+step, and no home-manager channel is needed.

flake.nix

@@ -11,21 +11,19 @@
     let
       lib = nixpkgs.lib;
       system = "x86_64-linux";
-      pkgs = import nixpkgs {
-        inherit system;
-        config.allowUnfree = true;
-      };
     in {
       nixosConfigurations = {
         nixos = lib.nixosSystem {
           inherit system;
-	  modules = [./configuration.nix];
-	};
-      };
-      homeConfigurations = {
-        leo = home-manager.lib.homeManagerConfiguration {
-	  inherit pkgs;
-          modules = [ ./home.nix ];
+          modules = [
+            ./configuration.nix
+            home-manager.nixosModules.home-manager
+            {
+              home-manager.useGlobalPkgs = true;
+              home-manager.useUserPackages = true;
+              home-manager.users.leo = import ./home.nix;
+            }
+          ];
         };
       };
     };

home.nix

@@ -1,10 +1,8 @@
 { config, pkgs, ... }:
 
 {
-  # Home Manager needs a bit of information about you and the paths it should
-  # manage.
-  home.username = "leo";
-  home.homeDirectory = "/home/leo";
+  # home.username and home.homeDirectory are set automatically by the
+  # Home Manager NixOS module, from the home-manager.users.<name> attribute.
 
   # This value determines the Home Manager release that your configuration is
   # compatible with. This helps avoid breakage when a new Home Manager release
@@ -109,7 +107,4 @@
       count = "ls -1 | wc -l";
     };
   };
-
-  # Let Home Manager install and manage itself.
-  programs.home-manager.enable = true;
 }