fedora-remote: minimal headless GNOME Remote Desktop host with Kanidm

New image built from upstream base-atomic (no desktop), adding only gnome-shell
+ gdm + gnome-remote-desktop + pipewire/portal + foot + Flatpak + Kanidm.
recommends=false to stay lean. Configures GNOME Remote Desktop headless remote
login on first boot (TLS + credentials + enable). Firefox preinstalled as a
per-user Flatpak. Add it to the CI matrix and prune both images.

images/fedora-remote/files/kanidm-nsswitch.conf

@@ -0,0 +1,14 @@
+passwd:     kanidm compat systemd
+group:      kanidm compat systemd
+shadow:     files
+hosts:      files dns myhostname
+services:   files
+netgroup:   files
+automount:  files
+aliases:    files
+ethers:     files
+gshadow:    files
+networks:   files dns
+protocols:  files
+publickey:  files
+rpc:        files