Bump version to 0.0.3

Polish icons, notification, number formatting; add release APK build

- Regenerate launcher foreground PNGs with more padding (57% of canvas)
- Change icon background to white
- Fix notification icons: proper white-on-alpha RGBA format
- Notification now shows state as title instead of redundant 'Levin'
- Format books count with locale-aware thousands separators
- Add release APK build (debug-signed) alongside debug APK in CI
- Enable 16 KB page alignment for Android 15 compatibility
- Bump version to 0.0.2

Fix CI: add contents:write permission for release uploads