Migrate to flakes

modules/software.nix

@@ -1,10 +1,10 @@
-{ config, lib, pkgs, ... }:
+{ config, lib, pkgs, inputs, ... }:
 
 with pkgs;
 
 let
   emacs-vterm = ((emacsPackagesNgGen emacsPgtkGcc).emacsWithPackages
-    (epkgs: with epkgs; [ vterm ]));
+    (epkgs: [ epkgs.vterm ]));
 
 in {
   environment.systemPackages = [
@@ -16,6 +16,7 @@ in {
     pass-wayland
     passff-host
     gitAndTools.pass-git-helper
+    inputs.agenix.defaultPackage.x86_64-linux
     # Browsers
     firefox
     ungoogled-chromium
@@ -83,7 +84,7 @@ in {
     shfmt
     ## Nix
     nixfmt
-    niv
+    rnix-lsp
     ## Python
     nodePackages.pyright
     black