refactor: share common files between images; trim fedora-remote for a VM

- Move Kanidm/flatpak/finalize.d/sshd files to images/shared/{files,repos}
  and have build.sh overlay them for every image.
- fedora-remote: aggressive hardware trim (no firmware, no kernel-modules-extra,
  no non-QEMU guest agents), keep + enable qemu-guest-agent (Proxmox).
- Fixes the missing package-list (release step) for fedora-remote.

images/fedora-remote/files/50-grd.preset

@@ -1,4 +1,5 @@
-# GNOME Remote Desktop headless remote login.
+# GNOME Remote Desktop headless remote login + Proxmox guest agent.
 enable gdm.service
 enable gnome-remote-desktop.service
 enable grd-firstboot.service
+enable qemu-guest-agent.service