feat(home): create XDG user directories by default

Enable xdg.userDirs with createDirectories so a fresh install lands with
Downloads/Documents/Pictures/Music/Videos/Desktop/Public/Templates (plus
home-manager's Projects) present and written to user-dirs.dirs, rather
than appearing only on first app use. mkDefault so a downstream home.nix
can flip it off or remap individual paths.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

modules/home/default.nix

@@ -1,7 +1,7 @@
 # Nomarchy — Home Manager entry point.
 # Consume this via homeModules.nomarchy (flake.nix), which also pulls in
 # the stylix home module that stylix.nix configures.
-{ config, pkgs, ... }:
+{ config, lib, pkgs, ... }:
 
 {
   imports = [
@@ -33,6 +33,16 @@
   services.network-manager-applet.enable = true;
   xsession.preferStatusNotifierItems = true;
 
+  # Standard XDG user directories (Downloads, Documents, Pictures, Music,
+  # Videos, Desktop, Public, Templates): written to user-dirs.dirs so file
+  # pickers/browsers resolve them, and created on activation so a fresh
+  # install lands with them present (not just on first app use). mkDefault
+  # so a downstream home.nix can flip it off or remap individual paths.
+  xdg.userDirs = {
+    enable = lib.mkDefault true;
+    createDirectories = lib.mkDefault true;
+  };
+
   home.stateVersion = "26.05";
 
   home.packages = with pkgs; [