GNOME Settings 51 shows the Users page's "Fingerprint Login" row only when
GDM's org.gnome.login-screen schema exists and its
enable-fingerprint-authentication key is true. The Phosh image logs in
through greetd/phrog, so without GDM the row never appeared and no finger
could be enrolled from the GUI; Settings never asked fingerprintd.
fp6-login-screen-schema installs GDM's schema file, unchanged, from
Alpine's gdm-48.0-r8, and nothing else of GDM. It is the only key Settings
reads, and nothing else on the image looks the schema up. replaces="gdm"
keeps a single copy if GDM is ever installed as well (tested in alpine:edge
in both orders; glib-compile-schemas stays clean). Added to the Phosh
image's packages.
Tested on the dev phone: the row appears, a thumb enrolled through
Settings' dialog, and it unlocks the lock screen.
