Bump openai from 4.104.0 to 6.3.0 in /backend

Bumps [openai](https://github.com/openai/openai-node) from 4.104.0 to 6.3.0.
- [Release notes](https://github.com/openai/openai-node/releases)
- [Changelog](https://github.com/openai/openai-node/blob/master/CHANGELOG.md)
- [Commits](openai/openai-node@v4.104.0...v6.3.0)

---
updated-dependencies:
- dependency-name: openai
  dependency-version: 6.3.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

backend/package-lock.json

@@ -81,7 +81,7 @@
     "jsonstream": "npm:JSONStream@^1.3.5",
     "jsonwebtoken": "^9.0.2",
     "lodash": "^4.17.21",
-    "openai": "^4.12.1",
+    "openai": "^6.3.0",
     "pg": "^8.8.0",
     "pg-query-stream": "^4.3.0",
     "postmark": "^4.0.4",