Support offline mode with local models

[skylab-styx-venus]

Describe the feature or problem you'd like to solve

Add ability to use Copilot CLI in air gapped environments with locally running models

Proposed solution

Copilot CLI cannot be used in air gapped or offline environments. While, the SDK offers the ability to add custom providers, it still expects larger GitHub connectivity.

I'd like support for an entirely offline mode that allows me to use the native Copilot CLI experience with a custom model that I am running locally.

This provides several benefits:

• Complete control of my data as I control the model and can turn off connectivity to GitHub
• Teams that develop code with GitHub connectivity can deploy code to offline environments and use the CLI's great features to support offline production deployments using a local model
• The SDK is great, but I want offline support natively in the CLI as it's a fantastic terminal UI

Example prompts or workflows

No response

Additional context

No response