Undo bulk search&replace

Provide the ability to undo an incorrect/accidental bulk search and replace.

As requested:
'One possible future request for Self-service disaster recovery:
A feature to help recover a batch of content from a bad "find & replace" job'

The issue names no files, tests, or entry points; begin by locating the existing bulk search-and-replace flow and reviewing how content changes are recorded. Define the recovery scope and completion criteria with maintainers before implementation, including how an accidental batch is identified and restored.

Written by the indexing model from the issue text.