chore(deps): bump openai from 2.1.0 to 2.3.0 in /backend

Bumps [openai](https://github.com/openai/openai-python) from 2.1.0 to 2.3.0.
- [Release notes](https://github.com/openai/openai-python/releases)
- [Changelog](https://github.com/openai/openai-python/blob/main/CHANGELOG.md)
- [Commits](openai/openai-python@v2.1.0...v2.3.0)

---
updated-dependencies:
- dependency-name: openai
  dependency-version: 2.3.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

backend/requirements.txt

@@ -49,7 +49,7 @@ fast-langdetect==1.0.0
 
 # LLM Integration
 anthropic==0.69.0
-openai==2.1.0
+openai==2.3.0
 
 # Observability
 langfuse==3.6.1