## Context

Add Project::default_path_list and reuse it for agent session work
directories and ACP server startup so agent processes start in the
project context by default

We previously removed all cwd from this hoping to have a global process
shared, but it doesn't work for remote projects. Since we're at the
project boundary anyway, we might as well start it up in a similar spot
as a new thread.


## 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:

- acp: Make sure the agent server is started in a project directory