Add REST endpoints to submit/fetch playground config between frontend ↔️ java-service

Summary

Expose endpoints so the frontend can send the playground configuration to the Java service and retrieve the effective configuration currently in use. Persist/track the config so the service runs with the submitted values.

Endpoints

GET /api/scop/playground/config → returns effective config in the same nested shape plus metadata.

POST /api/scop/playground/config → accepts the nested JSON above, validates, persists, and applies (or schedules) it.