The one-way migration 20261108140000_move_zjazd_tags_to_meetings gives
every material tagged zjazd-N without a meeting meeting N (the lowest
when it has several), never overwrites a meeting_id, logs tags naming a
missing meeting or disagreeing with meeting_id at Warn, and deletes the
exact zjazd-N tags; their links go through ON DELETE CASCADE. Rollback
is a no-op: the backup is the pg_dump taken before migrate.
