v2.12.1

Fixed

• Leave days were wiped on every restart. _async_save wrote the HA store
  version into the payload's schema_version field, which is always 1, so the
  v1→v2 migration ran on every load and never converged. That migration rebuilt
  leave_records from history alone, keeping only sick days — so vacation,
  off, flex, work-from-home, red days and squeeze days were discarded each time,
  and sick days went with them on the following restart.

  The migration now merges into the existing leave_records instead of
  replacing it, carries over every key it does not touch, and the saved
  schema_version is a real schema constant, so it runs once and stops.

• Arrival and departure margins, and the Google Sheets sync fingerprints, were
  dropped by the same migration. Both are preserved now.

Days already lost cannot be recovered — they are gone from storage. Re-enter a
stretch with worktime_tracker.set_period, then run
worktime_tracker.export_all to bring Google Sheets back in line.