One app for both events and tasks, talking directly to Nextcloud's CalDAV
endpoint - no DAVx5, no Google Play Services, no third-party services.
Encrypted at rest (SQLCipher DB, EncryptedSharedPreferences, Keystore-backed
widget state), HTTPS-only networking, home screen widgets, reminders,
subtasks, and full VTODO field support (status/priority/%complete/location/url).
