Proposal: Persist Record Edit State when Edit Form Fails

### Feature Request

### Problem / Opportunity

Related to #9930

If a book page edit submission fails due to an unexpected error, the changes that were made are lost forever. It is extremely frustrating to editors when this happens.

### Proposal

Instead of throwing away this work, let's improve the error handling/messaging and preserve the changes made by failed edits.

### 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

- @tfmorris
- @seabelis
- @bilch
- @akramcodez

### 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.

Start with the common Endpoints map and related issue #9930, then locate the book-page edit submission and its error handling. The issue does not name implementation files or tests; completion would require preserving changes after an unexpected failure and improving the resulting error messaging.

Written by the indexing model from the issue text.