mount: keep a link change's ctime in the dirty entry

The flush does not restamp times, so a dirty entry carrying an earlier
write's ctime moved the filer's ctime back from the link or unlink.

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

weed/mount/weedfs_link.go

@@ -255,6 +255,9 @@ func (fh *FileHandle) adoptLinkChangeLocked(stored *filer_pb.Entry, versionTsNs
 		fh.UpdateEntry(func(entry *filer_pb.Entry) {
 			entry.Name = linked.Name
 			entry.HardLinkId, entry.HardLinkCounter = linked.HardLinkId, linked.HardLinkCounter
+			if a, b := entry.Attributes, linked.Attributes; a != nil && b != nil && (b.Ctime > a.Ctime || b.Ctime == a.Ctime && b.CtimeNs > a.CtimeNs) {
+				a.Ctime, a.CtimeNs = b.Ctime, b.CtimeNs
+			}
 		})
 	} else {
 		fh.SetEntry(proto.Clone(linked).(*filer_pb.Entry))