feat(master): UPDATE_STATUS from the dashboard, logged when it changes

Appended message ID 50 (dashboard -> master): the update check's state and a
one-line summary. Master logs it whenever the summary changes, so the first
one after master starts says when an update is out.

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

dCommon/dEnums/MessageType/Master.h

@@ -102,5 +102,8 @@ namespace MessageType {
 		WORLD_RELOAD,
 		// Master -> dashboard: each running zone's files, whether they changed on disk, and which instances are stale
 		WORLD_FILES_STATUS,
+
+		// Dashboard -> master: what the update check found about this build (see UpdateStatus.h), for master's log
+		UPDATE_STATUS,
 	};
 }