build(deps): update google-genai requirement in /server/ai-gateway

Updates the requirements on [google-genai](https://github.com/googleapis/python-genai) to permit the latest version.
- [Release notes](https://github.com/googleapis/python-genai/releases)
- [Changelog](https://github.com/googleapis/python-genai/blob/main/CHANGELOG.md)
- [Commits](googleapis/python-genai@v1.0.0...v2.16.0)

---
updated-dependencies:
- dependency-name: google-genai
  dependency-version: 2.16.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

server/ai-gateway/requirements.txt

@@ -8,5 +8,5 @@ python-jose[cryptography]>=3.3.0
 httpx>=0.27.0
 python-dotenv>=1.0.0
 python-json-logger>=2.0.0,<4.0.0
-google-genai>=1.0.0
+google-genai>=2.16.0
 python-multipart>=0.0.7