Enable Backup & Restore setting in Settings screen

[Noro18]

Description

The Backup & Restore setting allows users to export/import their order data. Currently commented out and only shows a Toast - not actually functional.

File: app/src/main/java/com/example/ordermanagementcake/ui/settings/SettingsScreen.kt (lines 121-123)

Expected Behavior

Users can back up all app data (orders, clients, cakes) to a file and restore from a previously saved backup file.

Implementation

1. Uncomment the SettingsItem(Backup & Restore, ...) entry in supportItems.
2. Backup: Export all Room database tables (orders, clients, cakes, etc.) to a JSON or SQLite file.
   • Use SAF (Storage Access Framework) to let the user pick a save location.
   • Serialize data using Gson/Moshi or copy the Room database file directly.
3. Restore: Import data from a backup file.
   • Use SAF to let the user pick a file.
   • Parse and insert data back into the Room database (handle conflicts, offer overwrite/skip options).
4. Show progress indicators during backup/restore operations.
5. Add error handling for corrupted files, incompatible versions, and permission denials.
6. Consider adding a confirmation dialog before overwriting existing data on restore.

Additional Context

• BackupRestoreSheet exists at app/src/main/java/com/example/ordermanagementcake/ui/setting_options/BackupRestoreSheet.kt - review and update as needed.
• Room database entities are likely in the data/ package - check for Order, Client, Cake entities.