feat(installer): Skip login manager when unl0kr handles the passphrase

unl0kr already prompts for the LUKS passphrase on screen, so a login
manager on top of it would be a second prompt. The login screen now only
collects a fallback (none/greetd/sddm/gdm) when unl0kr is selected;
resolve_login_manager applies it only when install_unl0kr falls back to
the systemd initramfs, and the summary shows both states.

Also ships /etc/unl0kr.conf (breezy-dark) plus the empty
/usr/share/unl0kr/unl0kr.conf the package omits so unl0kr stops warning
about an unparseable config, and pins Hyprland in the user's
AccountsService record so gdm autologin does not fall back to
gnome.desktop.

AGENTS.md

@@ -74,7 +74,7 @@ The airootfs overlay ships it as `/usr/local/bin/alvin-install` (mode `0755` for
   locale, login manager, sshd, summary) then a fixed order of `install_*` steps
   (partition → LUKS → format/mount → pacstrap → fstab → repos → timezone → locale →
   hostname → network → sshd → user → git/SSH → end-4 dots → mkinitcpio → bootloader →
-  TPM/unl0kr → login manager → autologin → update (reflector + keyrings + `pacman -Syu`, warn-only) → cleanup). Screens and install steps are
+  TPM/unl0kr → login manager (none if unl0kr succeeded; with unl0kr selected the login screen only asks for a fallback) → autologin → update (reflector + keyrings + `pacman -Syu`, warn-only) → cleanup). Screens and install steps are
   independent — edit one without
   touching the other. An `EXIT` trap unmounts `$TARGET` and closes `cryptroot` on any exit.
 - **Package list**: `install_pacstrap` builds the *installed* system's list from the medium's