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/calamares/settings.conf

@@ -35,7 +35,12 @@ sequence:
     - users
     - networkcfg
     - hwclock
-    - packages
+    # packages module removed: it set update_db:true with no
+    # skip_if_no_internet/ignore_update_db_error, so an offline install (the
+    # exact case bos-welcome's nmtui step exists for) aborted here with a
+    # fatal pacman -Sy failure. Its only try_install packages (pipewire-pulse,
+    # pipewire-alsa) are already in packages.x86_64 and installed by
+    # unpackfs, so the step did nothing useful even when it succeeded.
     # archiso strips the kernel from the squashfs; stage it, drop the archiso
     # initramfs config, and write a stock mkinitcpio preset before initcpio runs.
     - shellprocess@kernel