filer.remote.sync: keep the resume position for the retry when its write fails

The retry in the same process now resumes from the position the ended
subscription returned, as filer.backup does, so a failed offset write
followed by an empty read cannot recompute -timeAgo past a failed event.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

weed/command/filer_remote_sync.go

@@ -22,6 +22,7 @@ type RemoteSyncOptions struct {
 	dir                *string
 	clientId           int32
 	clientEpoch        int32
+	resumeTsNs         int64
 }
 
 var _ = filer_pb.FilerClient(&RemoteSyncOptions{})