acp: Support terminal auth methods (#51999)

## Context

Brings in support for the new terminal auth methods. Currently behind
AcpBeta feature flag while the RFD stabilizes

## Self-Review Checklist

<!-- Check before requesting review: -->
- [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:

- N/A
d1177dc43cBen Brandt committed on 3/20/2026, 10:12:00 AM· committed by GitHubparentb45534a
7 files changedLine totals unavailable