Cross Plattform Sync

Introduce an optional cross-platform synchronization service that allows users to seamlessly sync their data across Apple and Android devices.

Currently, Budget Flow uses iCloud for synchronization between Apple devices, while data on Android is stored locally.

The new synchronization service should:

• Support cross-platform syncing: Keep data synchronized across Apple and Android devices.

• Support shared budget books: Allow users to share and collaboratively manage budget books across different platforms.

• Remain optional: Users should be able to decide whether they want to enable cross-platform synchronization or keep their data local.

• Preserve iCloud support: Apple users should continue to have the option to use iCloud instead of the new cross-platform synchronization service.

Users should be able to choose between local storage, iCloud (on Apple devices), or cross-platform sync, depending on their preferences and needs.