docs: add Tuning Engines OpenAI-compatible example

[cerebrixos]

Description

Adds Tuning Engines to the OpenAI API-compatible provider docs. The example uses Continue's existing provider: openai plus apiBase configuration path, so this is documentation-only and does not add a new provider enum.

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Checklist

• I've read the contributing guide
• The relevant docs, if any, have been updated or created
• The relevant tests, if any, have been updated or created

Screen recording or screenshot

N/A; docs-only change.

Tests

Not run; docs-only change to a model provider configuration page.

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Summary by cubic

Adds Tuning Engines to the OpenAI‑compatible provider docs. Includes a config example using the existing openai provider with apiBase https://api.tuningengines.com/v1 and a workspace inference key.

^{Written for commit 98e761e. Summary will update on new commits. Review in cubic}

[github-actions]

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I have read the CLA Document and I hereby sign the CLA

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[cubic-dev-ai]

No issues found across 1 file

_{Re-trigger cubic}

[cerebrixos]

I have read the CLA Document and I hereby sign the CLA (Venkat Chandra)

[cerebrixos]

I have read the CLA Document and I hereby sign the CLA

[cerebrixos]

recheck