Exit 1 when a deletion prompt is not confirmed (closes #423)

prune, snapshot purge, snapshot remove and database delete exited 0 when their confirmation prompt was declined or left unanswered, so a script could not tell that nothing was deleted. They now end with "deletion not confirmed" and exit 1. The [y/N] prompts accept y or Y; database delete still asks for yes.

Model: opus-5-5

internal/vaultik/snapshot.go

@@ -881,17 +881,12 @@ func (v *Vaultik) confirmAndExecutePurge(
 
 		var confirm string
 
+		// A failure to read the answer means no confirmation.
 		_, err := v.scanStdin(&confirm)
-		if err != nil {
+		if err != nil || strings.ToLower(confirm) != "y" {
 			v.printlnStdout("Cancelled")
 
-			return nil //nolint:nilerr // treat EOF or read error as "no"
-		}
-
-		if strings.ToLower(confirm) != "y" {
-			v.printlnStdout("Cancelled")
-
-			return nil
+			return ErrNotConfirmed
 		}
 	} else if !quiet {
 		v.UI.Infof("The following snapshots will be deleted:")
@@ -1490,7 +1485,7 @@ func (v *Vaultik) RemoveSnapshot(
 	}
 
 	if !v.confirmRemoveSnapshot(snapshotID, opts) {
-		return result, nil
+		return result, ErrNotConfirmed
 	}
 
 	// Checked before the local record is deleted: it may be the last