Enhancement Cross-Platform Synchronization for NeoRoo using d2 library

NeoRoo currently talks to DHIS2 through raw HTTP calls with no offline support, so if a nurse loses connectivity while entering baby data, that data is just gone. I'm proposing to integrate the d2 Android SDK as the primary sync engine and build a Flutter abstraction layer on top of it that works across both Android and iOS. The main deliverables are: a Pigeon-based platform bridge to d2 (Android) and DHIS2 REST API (iOS), an offline-first sync queue using Drift/SQLite with automatic retry, a server-wins conflict resolution system with a review log, real-time sync status indicators in the UI, background sync with battery optimization, push notifications for server-side changes, and a testing + monitoring toolkit. By the end, healthcare workers should be able to use NeoRoo reliably regardless of connectivity.