[Feature] Support github-copilot/... as a model provider

[dengxifeng]

Hi, thanks for building summarize — very useful tool.

Could you support github-copilot/... model ids, for example:

summarize "https://example.com" --model "github-copilot/claude-haiku-4.5"

Right now this fails with:

Unsupported model provider "github-copilot"

This would be useful for users who already have GitHub Copilot authenticated and want to use summarize without setting up another API key.

Even an experimental or CLI-bridge-based implementation would be helpful.

Thanks!