Copilot model picker adds Sonnet 4.6, Opus 4.7, and Gemini 3.1 Pro

GitHub Copilot Chat now exposes Claude Sonnet 4.6, Opus 4.7, Haiku 4.5, GPT-5 mini, Gemini 3.1 Pro, and Gemini 3 Flash alongside the default GPT-5. Available on Pro, Business, and Enterprise.