Bump openai from 1.109.1 to 2.0.1 in /backend (#2348)

Bumps [openai](https://github.com/openai/openai-python) from 1.109.1 to 2.0.1.
- [Release notes](https://github.com/openai/openai-python/releases)
- [Changelog](https://github.com/openai/openai-python/blob/main/CHANGELOG.md)
- [Commits](openai/openai-python@v1.109.1...v2.0.1)

---
updated-dependencies:
- dependency-name: openai
  dependency-version: 2.0.1
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

backend/poetry.lock

@@ -29,7 +29,7 @@ langchain = "^0.3.26"
 langchain-community = "^0.3.26"
 lxml = "^6.0.0"
 markdown = "^3.7"
-openai = "^1.109.0"
+openai = "^2.0.1"
 owasp-schema = "^0.1.10"
 pgvector = "^0.4.1"
 psycopg2-binary = "^2.9.9"