feat(dev): deploy claude-code config via systemd instead of home-manager

Home-manager fails on the dev microVM because nix-env --set needs
writable nix state dirs, but the microVM shares /nix/store read-only
via virtiofs.

Extract shared claude-code settings into settings.nix, add a NixOS
module (nixos.nix) that deploys the same files via a systemd oneshot
service with RequiresMountsFor to handle virtiofs mount ordering.
The nb host continues using home-manager unchanged.

hosts/dev/configuration.nix

@@ -29,6 +29,7 @@ in
 {
   imports = [
     ./modules/dev-tools.nix
+    ./users
   ];
 
   networking.hostName = "dev";

hosts/dev/users/default.nix

@@ -0,0 +1,3 @@
+{
+  imports = [ ./dominik.nix ];
+}

hosts/dev/users/dominik.nix

@@ -0,0 +1,6 @@
+{ config, lib, pkgs, ... }:
+{
+  imports = [
+    ../utils/home-manager/claude-code/nixos.nix
+  ];
+}