When using dev containers, copilot uses `~/.copilot` within the container

- Copilot Chat Extension Version: There is no separate extension anymore?
- VS Code Version: 1.129.1
- OS Version: Linux mint 22.3
- Feature (e.g. agent/edit/ask mode): Custom agents
- Selected model (e.g. GPT 4.1, Claude 3.7 Sonnet): -
- Logs: -

Steps to Reproduce:

1. Create a new agent in ~/.copilot.
2. Check the dev container file system. You will find the new agent there instead of on the host.

Given that the whole point of putting agents into the home directory is sharing them, it seems to me that the host file system should be used for this feature.