feat: Flake | use home-manager as a nixos module

nixos/configuration.nix

@@ -1,7 +1,7 @@
 # Edit this configuration file to define what should be installed on
 # your system.  Help is available in the configuration.nix(5) man page
 # and in the NixOS manual (accessible by running ‘nixos-help’).
-{lib, ...}: {
+{lib, config, pkgs, ...}: {
   imports = [
     ./imports/environment.nix
     ./imports/hardware.nix
@@ -40,6 +40,8 @@
     };
   };
 
+  home-manager.users.shahab = import ../home-manager/home.nix;
+
   # This value determines the NixOS release from which the default
   # settings for stateful data, like file locations and database versions
   # on your system were taken. It‘s perfectly fine and recommended to leave