Closes #25594

This PR fixes an issue where signing into Copilot required restarting
Zed.

Copilot depends on an OAuth token that comes from either `hosts.json` or
`apps.json`. Initially, both files don't exist. If neither file is
found, we fallback to watching `hosts.json` for updates. However, if the
auth process creates `apps.json`, we won't receive updates from it,
causing the UI to remain outdated.

This PR fixes that by watching the parent `github-copilot` directory
instead, which will always contain one of those files along with an
additional version file.

I have tested this on macOS and Linux Wayland.

Release Notes:

- Fixed an issue where signing into Copilot required restarting Zed.