Wrapper around dataExportService that creates and verifies a full SREF
backup before the v2->v1 categories migration. Throws on any failure to
ensure migration aborts cleanly.
- Generates filename <ProfileName>_avant-migration-<ISO8601>.sref
- Writes to ~/Documents/Simpl-Resultat/backups/ (creates dir if missing)
- Verifies integrity via re-read + SHA-256 checksum
- Reuses profile PIN for encryption when protected
- Adds two minimal Tauri commands: ensure_backup_dir, get_file_size
- Stable error codes (BackupError) to map to i18n keys in the UI layer
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>