rename gpt-4o-mini and gpt-4.1-mini

for consistency with other names, even though there's only one variant

`gpt-4o-mini` ➡️️ `gpt-4o-mini-2024-07-18`
`gpt-4.1-mini` ➡️️ `gpt-4.1-mini-2025-04-14`

https://platform.openai.com/docs/models/gpt-4o-mini
https://platform.openai.com/docs/models/gpt-4.1-mini