docs: add Tuning Engines endpoint example

[cerebrixos]

Adds a Tuning Engines custom AI endpoint example for LibreChat's librechat.yaml configuration. The example uses the OpenAI-compatible base URL, tenant-scoped inference key, and model aliases enabled in Tuning Engines.

[vercel]

@bazooka720 is attempting to deploy a commit to the LibreChat's projects Team on Vercel.

A member of the Team first needs to authorize it.

[cerebrixos]

Note for maintainers: this is a docs-only PR. The visible Vercel failure is fork preview-deploy authorization, not a docs/build failure. I can adjust the placement or wording if there is a preferred location for custom OpenAI-compatible gateway examples.

[cerebrixos]

Hello team @DenisPalnitsky . Please do consider this PR for merge. So much appreciate in advance :)

[berry-13]

@cerebrixos You’ll first need to open a PR in the LibreChat repo. The AI Providers section is reserved for officially supported endpoints with custom icons.

That said, I don’t consider this provider mature or trusted enough at the moment, so I wouldn’t recommend opening a PR for it

[cerebrixos]

Thanks @berry-13 No problem. We will revert back in 2-3 months and hopefully more credible at the time. Thanks for considering