Implement SqlCafeRepository with CRUD operations and timeline event
creation. Add CafesClient for CLI HTTP access. Wire cafes into backup
export/restore and empty-database verification.
- Add BackupData struct and BackupService with raw SQL export/import
- Restore uses raw inserts to bypass brew deductions and timeline creation
- Restore requires an empty database, inserts in FK dependency order
- Add comprehensive e2e test verifying full round-trip fidelity