Print a failed command's error once on stderr (closes #433)

A failed command printed its error twice on stderr: as an ERROR log record and as the final ERROR: line the README documents. The command handlers, a restore failure that ends the command and a failed blob upload now log that error at info level or not at all, so without --verbose or --debug only the final line appears.

Model: opus-5-5

internal/cli/app.go

@@ -337,7 +337,7 @@ func runVaultikApp(
 		},
 		Mode: mode,
 	}, op, func(err error) {
-		log.Error(failMsg, "error", err)
+		log.Info(failMsg, "error", err)
 		ReportErrorf("%s: %v", failMsg, err)
 	})
 }