OpenAPI spec not validated against actual route implementations in CI

[Haroldwonder]

The api/src/openapi-generator.ts generates an OpenAPI spec but there is no CI step that validates the generated spec against the actual route implementations. Routes can drift from the spec without detection.

File: api/src/openapi-generator.ts, CI workflow

Fix: Add a CI step that generates the OpenAPI spec and compares it against the committed spec file, failing if there are differences.