The notify-on-status-change alert now offers a Reveal button that
jumps to the session whose status changed, shown only when the
session can still be resolved.

Replace the frozen per-window snapshot with a running
lastSeenStatusText baseline so a window watch covers every session
in the window, including ones created after it was armed. Session
scope keeps a one-shot arm-time baseline that folds in any in-flight
change so arming within a debounce window does not fire spuriously.