Move Nix files back to the root of the project

lib/shared/home-manager-packages.nix

@@ -0,0 +1,35 @@
+{
+  headless,
+  pkgs,
+  username,
+  ...
+}:
+
+with pkgs;
+[
+  cachix
+  delta
+  entr
+  gcc
+  git
+  git-crypt
+  gnupg
+  inotify-tools
+  jq
+  killall
+  lua
+  mob
+  pv
+  simple-http-server
+  sshs
+  tldr
+  tree
+  tree-sitter
+  unzip
+  w3m
+  watchexec
+  wget
+  xclip
+  xdg-utils
+  zbar
+]

lib/shared/home-manager.nix

@@ -0,0 +1,24 @@
+{ username, ... }:
+
+{
+  home.username = "${username}";
+  home.homeDirectory = "/home/${username}";
+
+  # Nicely reload system units when changing configs.
+  systemd.user.startServices = "sd-switch";
+
+  # See https://github.com/nix-community/home-manager/issues/2064#issuecomment-2259307514.
+  # This is a workaround for the following errors that appeared when switching back to unstable:
+  # - 1: Failed to start unit flameshot.service
+  # - 2: org.freedesktop.systemd1.NoSuchUnit: Unit tray.target not found.
+  systemd.user.targets.tray = {
+    Unit = {
+      Description = "Home Manager System Tray";
+      Requires = [ "graphical-session-pre.target" ];
+    };
+  };
+
+  home.stateVersion = "22.05";
+
+  programs.home-manager.enable = true;
+}