Add to your flake.nix:
inputs.dotfiles.url = "github:aspiand/dotfiles";overlays.default exposes every package, so pkgs.<name> is the same derivation as
nix build .#<name> — both built against this flake's nixpkgs.
{
nixpkgs.overlays = [ inputs.dotfiles.overlays.default ];
environment.systemPackages = with pkgs; [ hanabi 9router headroom ];
}{
home.packages = [ inputs.dotfiles.packages.${pkgs.stdenv.hostPlatform.system}.hanabi ];
}