351fe7a672
Added `/ping/sync` endpoint with timestamp-based Delta-Sync functionality to efficiently support offline-first clients. Extended `PingApi` and frontend clients (`PingApiClient`, `PingApiKoinClient`) with `syncPings`. Updated repository, service, and controller logic for sync handling, including new JPA query `findByCreatedAtAfter`. Adjusted test doubles and completed unit tests for backend and frontend alignment. Documented sync approach and API usage.