[breaking] Google deprecates gemini-3.1-flash-lite-preview

gemini-3.1-flash-lite-preview was announced May 7, 2026 (deprecating 5/11/26) with shutdown May 25, 2026. Replacement: gemini-3.1-flash-lite. Effective: 2026-05-25. Migration target: google/gemini-3.1-flash-lite. Affected: google/gemini-3.1-flash-lite-preview. Severity: breaking. Verification: verified.