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/skel/.local/share/applications/breadsearch.desktop

@@ -0,0 +1,9 @@
+[Desktop Entry]
+Name=breadsearch
+Comment=Semantic system-wide search
+Exec=breadsearch
+Icon=system-search
+Terminal=false
+Type=Application
+Categories=Utility;
+StartupWMClass=breadsearch