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/snapshot_restore.go

@@ -104,7 +104,7 @@ func runRestore(cmd *cobra.Command, args []string, opts *RestoreOptions) error {
 			SkipErrors: rootFlags.SkipErrors,
 		})
 	}, func(err error) {
-		log.Error("Restore operation failed", "error", err)
+		log.Info("Restore operation failed", "error", err)
 		ReportErrorf("Restore failed: %v", err)
 	})
 }