fedora-remote: fix GDM greeter so headless RDP renders

The minimal base (recommends off) was missing session infrastructure and one
maintained service actively broke the greeter, so RDP clients saw only a white
screen:

- add dbus-daemon: gdm-wayland-session runs it for the greeter session bus
- add systemd-pam: pam_systemd starts the per-user systemd manager
- nsswitch: shadow must include systemd so pam_unix can resolve GDM 50's
  dynamic gdm-greeter user (Fedora 44 ships 'files systemd')
- mask uresourced: its resource tuning makes user@<uid>.service fail with
  'Failed to spawn executor', leaving no systemd user bus for gnome-session

images/shared/files/kanidm-nsswitch.conf

@@ -1,6 +1,6 @@
 passwd:     kanidm compat systemd
 group:      kanidm compat systemd
-shadow:     files
+shadow:     files systemd
 hosts:      files dns myhostname
 services:   files
 netgroup:   files