Security: liteLLM dependency vulnerable to supply chain attack (TeamPCP)

## Summary

The `gemini/evaluation/synthetic-data-evals/pyproject.toml` file specifies `litellm>=1.61.9` with no upper bound.

liteLLM versions **1.82.7** and **1.82.8** were compromised by the **TeamPCP** group via a supply chain attack through Trivy. Any `pip install` during the attack window (2026-03-23 to 2026-03-24) would have pulled the malicious version.

## Impact

The compromised versions steal sensitive credentials including SSH keys, AWS/GCP/K8s credentials, CI/CD tokens, and environment variables. Version 1.82.8 installs a `.pth` persistence mechanism that executes on **every Python startup** — even after liteLLM is uninstalled.

## Suggested Fix

```diff
- "litellm>=1.61.9",
+ "litellm>=1.61.9, <=1.82.6",
```

Note: `google/adk-python` already applied this fix on 2026-03-24 (commit `77f1c41b`).

I attempted to submit a PR but this repository limits PRs to collaborators only. The fix branch is available at: `gn00295120:fix/pin-litellm-supply-chain`

## References

- [BerriAI/litellm#24512](https://github.com/BerriAI/litellm/issues/24512) — Incident report
- [Wiz.io Analysis](https://www.wiz.io/blog/threes-a-crowd-teampcp-trojanizes-litellm-in-continuation-of-campaign) — Attack chain analysis
- [OSV: MAL-2026-2144](https://osv.dev/vulnerability/MAL-2026-2144) — Advisory