Merge UI should not allow merge if records have changed in the mean time

When a super librarian clicks on the merge button the underlying code will re-fetch all the works/docs and if there are any edits (since) the UI will inform them to refresh

### Evidence / Screenshot (if possible)

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### Steps to Reproduce

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2. Do ...

* Actual:
* Expected:

### Details

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- **Environment (prod/dev/local)?** prod

### Proposal & Constraints

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The issue names the merge button and the re-fetch of works and documents, but no files or tests. Start by locating the merge UI and its re-fetch path; done means edits made since the merge began prevent the merge and tell the super librarian to refresh.

Written by the indexing model from the issue text.