HazemDaw/spendo — reverse-engineered prompt

Build me a polished mobile personal finance app for Android and iPhone in Flutter. I want users to track income and expenses, add, edit, delete, and undo transactions, choose categories, and see a simple home screen with category icons around a donut style chart.

The app should work without internet first, saving everything locally, with optional login so people can sync and restore their data later. Add budgets with progress warnings, spending insights like biggest category, expensive days, period comparisons, and trends. Let users switch between day, week, month, year, all time, and custom date ranges.

Please include custom categories, dark mode, English and Russian language support, currency settings, receipt scanning that creates editable draft transactions, and export to PDF and CSV. Keep the code clean and easy to maintain, with separate areas for screens, business logic, storage, sync, settings, and tests. Look up current Flutter and Firebase docs online if needed.