- Created internal/progress/estimator.go with ETAEstimator component
- Tracks elapsed time and estimates remaining time based on progress
- Enhanced Spinner and LineByLine indicators to display ETA info
- Integrated into BackupCluster and RestoreCluster functions
- Display format: 'Operation | X/Y (Z%) | Elapsed: Xm | ETA: ~Ym remaining'
- Preserves spinner animation while showing progress/time estimates
- Quick Win approach: no historical data storage, just current operation tracking