Add coreutils to authentik container

The ak wrapper script requires mkdir (and likely other coreutils)
to create runtime directories.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

containers/authentik/default.nix

@@ -10,6 +10,7 @@ pkgs.dockerTools.buildLayeredImage {
   contents = [
     pkgs.authentik
     pkgs.bashInteractive
+    pkgs.coreutils
     pkgs.cacert
     pkgs.tzdata
   ];