feat(ipa/docker): grant docker access via IPA group membership

Create an IPA group "docker-access" (GID 50010) and pin the local
"docker" group to that GID on all Docker hosts.  Any IPA user in the
docker-access group automatically gains docker socket access through
SSSD supplementary-group resolution — no per-host docker.members
entry needed.

Specific changes:
- variables.nix: add dockerAccessGid = 50010
- modules/docker/enable-service.nix: lib.mkForce docker GID to
  dockerAccessGid, removing the need to name individual IPA users
- modules/build-types/docker.nix: remove direct wayne docker.members
  entry (access now comes from IPA group)
- modules/ipa/client.nix: refactor repeated security.* / systemd.*
  top-level keys into merged attribute sets (fixes statix W20); add
  security.pam.services.lightdm.makeHomeDir so the GUI login path
  also creates the home dir on first login

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

modules/build-types/docker.nix

@@ -33,9 +33,6 @@
   ];
 
   users.users.${vars.primaryUser}.extraGroups = [ "docker" ];
-  # Grant the IPA domain user docker access via the local group so that
-  # `wayne` can manage containers without sudo.
-  users.groups.docker.members = [ "wayne" ];
   services.openssh.settings.PermitRootLogin = "yes";
 
   networking.firewall.allowedTCPPorts = [