v0.9.0

* Google Play release: separate gplay build flavor with Android Auto Backup to Google Drive
* New "Back up to Google Drive" toggle in Settings (Play build only) to disable cloud backup
* F-Droid build keeps Auto Backup disabled (privacy-strict, unchanged behavior)
* Added Privacy policy link in Settings (mysportsmate.de/datenschutz-officebreak)
* Fixed crash from duplicate exercise names; duplicates now prevented (#30)
* Maintenance: updated build toolchain and dependencies
