Allow reversion of a single work or author after bulk merge

### Feature Request

### Problem / Opportunity

Sometimes incorrect records are merged. Usually this is with a bulk merge where all or most other merged records were merged correctly. Having the option for admins to select a single merged record from a bulk merge would be useful. Example, https://openlibrary.org/recentchanges/2025/07/18/merge-works/151730566, one title was incorrectly merged with a merge of six works. If I revert this, all will be reversed. I only want to revert the one, along with associated editions that were initially associated with that work.

Manually identifying and reverting records is time consuming. Sometimes this involves hundreds or thousands of records.

Success is when a single merge can be "cherry picked" from a bulk merge to be reverted.
### Proposal

### Breakdown

### Related files

Refer to [this map of common Endpoints](https://github.com/internetarchive/openlibrary/wiki/Endpoints):
*

### Requirements Checklist
Checklist of requirements that need to be satisfied in order for this issue to be closed:
* [ ]

### Stakeholders

*

### Instructions for Contributors

* **Before** [creating a new branch](https://github.com/internetarchive/openlibrary/wiki/Git-Cheat-Sheet#making-changes-and-creating-a-pull-request) or pushing up changes to a PR, please first [run these commands](https://github.com/internetarchive/openlibrary/wiki/Git-Cheat-Sheet#working-on-your-branch) to ensure your repository is up to date, as the pre-commit bot may add commits to your PRs upstream.

No implementation files, tests, or specific entry points are identified. Start with the common Endpoints map and the linked bulk-merge example, then determine how a single merged work and its associated editions could be selected for reversal. Done should mean one merge from a bulk operation can be reverted without reversing the others.

Written by the indexing model from the issue text.