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/fedora-remote/custom.yaml

@@ -26,6 +26,13 @@ packages:
   # grd-firstboot generates the RDP TLS certificate with the openssl CLI.
   - openssl
 
+  # GDM/gnome-session session infrastructure. The greeter needs the reference
+  # dbus-daemon for its session bus, and pam_systemd (systemd-pam) to start the
+  # per-user systemd manager; without them the greeter dies and RDP clients just
+  # get a white screen (base-atomic does not pull these in with recommends off).
+  - dbus-daemon
+  - systemd-pam
+
   # Kanidm Unix authentication (kanidm-unixd-clients pulls kanidm-clients).
   - kanidm-unixd-clients
 
@@ -76,6 +83,15 @@ postprocess:
       install -m 0644 /usr/share/fedora-remote/authselect/nsswitch.conf /etc/nsswitch.conf
     fi
 
+  # uresourced's resource tuning breaks the GDM greeter's systemd user manager
+  # here: user@<uid>.service fails with "Failed to spawn executor" (result
+  # 'resources'), so the greeter never registers and RDP clients get a white
+  # screen. It is optional, so mask it.
+  - |
+    #!/usr/bin/env bash
+    set -xeuo pipefail
+    ln -sf /dev/null /etc/systemd/system/uresourced.service
+
   # Kanidm SELinux policy (same approach as fedora-cosmic).
   - |
     #!/usr/bin/env bash

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