Bump openai-agents from 0.2.0 to 0.4.0

Bumps [openai-agents](https://github.com/openai/openai-agents-python) from 0.2.0 to 0.4.0.
- [Release notes](https://github.com/openai/openai-agents-python/releases)
- [Changelog](https://github.com/openai/openai-agents-python/blob/main/docs/release.md)
- [Commits](openai/openai-agents-python@v0.2.0...v0.4.0)

---
updated-dependencies:
- dependency-name: openai-agents
  dependency-version: 0.4.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

src/backend/requirements.txt

@@ -140,7 +140,7 @@ openai==1.96.1
     # via
     #   fastapi-app (pyproject.toml)
     #   openai-agents
-openai-agents==0.2.0
+openai-agents==0.4.0
     # via fastapi-app (pyproject.toml)
 opentelemetry-api==1.31.1
     # via