Remove outdated gemini-2.0-flash and gemini-1.5-pro.
Add gemini-2.5-flash-lite (GA) and the three Gemini 3.x preview
models (gemini-3.1-pro-preview, gemini-3-flash-preview,
gemini-3.1-flash-lite-preview). All have 1M token context windows.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>