Update default model to GPT-4.1

[azdanov]

Not an issue, but a heads up. Since GitHub swapped to GPT-4.1 as default: https://github.blog/changelog/2025-05-08-openai-gpt-4-1-is-now-generally-available-in-github-copilot-as-the-new-default-model/

I guess it's here that needs to be changed?

CopilotChat.nvim/lua/CopilotChat/config.lua

Line 64 in 7565325

model = 'gpt-4o', -- Default model to use, see ':CopilotChatModels' for available models (can be specified manually in prompt via $).

[deathbeam]

Yes, to gpt-4.1. feel free to make PR otherwise I can do it later