Own the workspace list in MultiWorkspace (#52546)

## Context

TODO

## Self-Review Checklist

<!-- Check before requesting review: -->
- [ ] I've reviewed my own diff for quality, security, and reliability
- [ ] Unsafe blocks (if any) have justifying comments
- [ ] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [ ] Tests cover the new/changed behavior
- [ ] Performance impact has been considered and is acceptable

Release Notes:

- N/A

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Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>
807207e27fMikayla Maki committed on 3/30/2026, 10:06:53 PM· committed by GitHubparentb48dd02
19 files changedLine totals unavailable