feat: TUI improvements and consistency fixes

- Add product branding header to main menu (version + tagline)
- Fix backup success/error report formatting consistency
- Remove extra newline before error box in backup_exec
- Align backup and restore completion screens

internal/tui/backup_exec.go

@@ -454,7 +454,6 @@ func (m BackupExecutionModel) View() string {
 	} else {
 		// Show completion summary with detailed stats
 		if m.err != nil {
-			s.WriteString("\n")
 			s.WriteString(errorStyle.Render("╔══════════════════════════════════════════════════════════════╗"))
 			s.WriteString("\n")
 			s.WriteString(errorStyle.Render("║              [FAIL] BACKUP FAILED                            ║"))