Fix boot-critical, session, and UX bugs found in round-3 UX audit

Snapshots panel was non-functional (wrong snapper flag); breadgreet picked
the wrong session .desktop and skipped bos-session's PATH fixup; Calamares
aborted offline installs over an unnecessary packages module; snapshot
rollback silently no-op'd on BOS's pinned-subvolume layout (now points at
grub-btrfs instead); breadcrumbs was configurable but had no daemon to run
it. Also: SUPER+I double-bind, breadpaper/packages panels blocking the GTK
main thread, dead polkit rule, and a sweep of smaller drift (default
sidebar view, stale wording, missing .desktop launchers, wallpaper daemon
not recording its own default).

iso/airootfs/etc/greetd/config.toml

@@ -2,11 +2,15 @@
 # squashfs and enabled by post-install.sh; the live ISO instead autologins
 # liveuser on tty1 (see getty@tty1 drop-in) so the installer comes straight up.
 #
-# tuigreet shows a minimal greeter, then launches the BOS Hyprland session via
-# bos-session (which fixes up PATH for the bakery bread apps).
+# breadgreet (bread-ecosystem's own greeter) is hosted under cage — a single-
+# client kiosk Wayland compositor, since greetd itself has no display of its
+# own — and speaks greetd's IPC directly. It resolves the session to launch
+# from /usr/share/wayland-sessions/bos.desktop, which points at bos-session
+# (fixes up PATH for the bakery bread apps; greetd starts no login shell, so
+# /etc/profile.d is never sourced otherwise).
 [terminal]
 vt = 1
 
 [default_session]
-command = "tuigreet --remember --time --cmd /usr/local/bin/bos-session"
+command = "cage -s -- breadgreet"
 user = "greeter"