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

A command that failed after startup wrote the error twice on stderr:
as an ERROR log record and as the final ERROR: line. The failure
handlers now log the failure at info level, so the record appears only
under --verbose or --debug, next to the records that led up to it.

A failed blob upload is logged at info level for the same reason. A
restore that stops on a file it cannot restore no longer logs that
file's error, which the final line carries; under --skip-errors it is
still logged.

Model: opus-5-5

internal/cli/info.go

@@ -39,7 +39,7 @@ func NewInfoCommand() *cobra.Command {
 			}, func(v *vaultik.Vaultik) error {
 				return v.ShowInfo()
 			}, func(err error) {
-				log.Error("Failed to show info", "error", err)
+				log.Info("Failed to show info", "error", err)
 				ReportErrorf("Failed to show info: %v", err)
 			})
 		},