docs: add TokenLab OpenAI-compatible client example

[hedging8563]

Summary

• Document TokenLab through Graphiti's existing OpenAIGenericClient base_url path.
• Keep the change docs-only and scoped to the project's existing OpenAI-compatible configuration surface.

Validation

• git diff --check

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Supersedes #1639. The previous PR was closed while fixing contributor commit metadata; this replacement branch preserves the same scoped diff with commits authored by hedging8563 <45883076+hedging8563@users.noreply.github.com>.

[zep-cla-assistant]

All contributors have signed the CLA ✍️ ✅
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[hedging8563]

I have read the CLA Document and I hereby sign the CLA behalf on myself, e-mail: cryptoninja2008@gmail.com

[hedging8563]

recheck