- A sign-out still finishing when someone signs in again stops after each
  step if a newer sign-in started, so it can't end the new session,
  delete its copy, or sign the user out again (Astra round 4).
- Whenever the signed-in account settles, at startup from the session
  Supabase restored (offline too) and on every account change, each copy
  keeps only that account's records, or none when signed out. A deletion
  a crash interrupted is finished on the next start. CloudAccountCopy's
  one method is now deleteAllExcept(CloudCopyScope? keep).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>