RongLei a37bc26ed3 fix: restore GitHub Copilot auth flow
Implement the real GitHub device flow and Copilot token exchange for the GitHub Copilot provider.

Also route github-copilot models through a dedicated backend and strip the provider prefix before API requests.

Add focused regression coverage for provider wiring and model normalization.

Generated with GitHub Copilot, GPT-5.4.
2026-04-02 03:46:40 +08:00
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2026-04-02 03:46:40 +08:00