acp: Support raw agent registry binaries (#58579)

It is valid to have raw binary paths in the registry but we didn't
handle them.

Self-Review Checklist:

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

Release Notes:

- acp: Fix for certain ACP Registry agent downloads not starting
8ce658ffa7Ben Brandt committed on 6/5/2026, 9:26:19 AM· committed by GitHubparent33d8c7e
2 files changedLine totals unavailable