docs: clarify enterprise settings required for Copilot App to work

### Short summary

_No response_

### Affected version or release

v1.0.10

### Installation context

mac-os

### What happened?

Attempting to use the app against a data residency domain in AU (ghe.com).

I'm getting "retry loading models" after authorisation has completed successfully and starting the first session.

I'm unclear which enterprise settings need to be enabled

- GitHub CLI is one,
- CLI remote control? Or will it fail gracefully with a subset of features available if this isn't set?
- Presumably not 'preview features' anymore now the app is GA?

Same local setup is fine with a personal account.

### Steps to reproduce

_No response_

### Expected behavior

_No response_

### Additional context

_No response_

Start by locating the documentation for using the Copilot App with an enterprise data residency domain such as ghe.com, then review the authorization and model-loading requirements. Clarify whether GitHub CLI, CLI remote control, or preview features must be enabled, and document the expected behavior when a setting is unavailable.

索引モデルが issue の本文から書いたものです。