Auto-sync Postman collection with OpenAPI schema on merge to main #1346

Problem

Our shared Postman collection is updated manually, so it often goes out of sync with the actual API. Teams end up using outdated endpoints, request bodies, or missing new APIs.

Proposed Solution

Add a GitHub Actions workflow that runs on every push to main (after merge) and:

1. Exports the OpenAPI schema using the existing backend/scripts/kaapi_export_openapi.py
2. Converts it to a Postman collection using openapi-to-postmanv2
3. Updates the shared team collection via the Postman API

This will be a separate workflow from the existing PR-level API Breaking Changes Check, so only merged changes reach Postman.