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/.config/breadlock/breadlock.example.toml

@@ -0,0 +1,22 @@
+# Copy to ~/.config/breadlock/breadlock.toml — every field is optional and
+# defaults to the value shown here if omitted or the file doesn't exist.
+
+[background]
+# "color" (bread-theme palette background) or "image" (a PNG, cover-fit)
+mode = "color"
+path = ""
+# v2 feature — accepted but currently just logs a warning and shows the
+# background unblurred (needs a wlr-screencopy capture, not implemented yet).
+blur = false
+
+[clock]
+# strftime format
+format = "%H:%M"
+
+[font]
+family = "Varela Round"
+
+[input]
+# How long the "wrong password" state (red pill) shows before input
+# re-enables, in milliseconds.
+fail_timeout_ms = 800