[breaking] Azure AI Foundry retires gpt-4o on 2026-03-31

Azure AI Foundry lists gpt-4o (2024-08-06-ev3) as deprecated with retirement on 2026-03-31; suggested replacement: gpt-5.1. Azure retirement dates are platform-specific and may differ from the model provider's own schedule. The page does not date the announcements; announced_at reflects the retirement date (already past at capture). Effective: 2026-03-31. Migration target: microsoft/gpt-5.1. Affected: microsoft/gpt-4o-2024-08-06-ev3. Severity: breaking. Verification: verified.