[Enhancement]: Allow user to provide custom model slug for OpenRouter

[ByteAtATime]

What features would you like to see added?

By its nature, OpenRouter keeps adding new models. It becomes tiring to have to wait for LibreChat to update to match (for example, I cannot use the new Gemini 2.5 model on OpenRouter). It would be great if I can provide a custom slug that is not in the list.

More details

I think that should be all the details!

Which components are impacted by your request?

UI

Pictures

No response

Code of Conduct

• I agree to follow this project's Code of Conduct

[danny-avila]

This is only when you are relying on a hosted instance instead of managing one yourself. This request may aptly fall under the existing issue, which is on the roadmap: #1028