refactor(mhfpacket): rename 15 Unk fields with identified meanings

Replace unknown field names with descriptive names based on handler
logic analysis, switch dispatch patterns, DB query context, and
inline comments:

- ObjectHandleID, IsQuest, ItemIDCount, MaxCount, TokenLength,
  FormatVersion, LogoutType (high confidence from comments/constants)
- QueryType, DataType, MissionIndex, CheckOnly, RequestType,
  ExchangeType, TournamentID (confirmed by handler switch/if usage)

Also fix MsgSysLogout.Build calling ReadUint8 instead of WriteUint8.

server/channelserver/handlers_helpers.go

@@ -70,7 +70,7 @@ func updateRights(s *Session) {
 		ClientRespAckHandle: 0,
 		Bitfield:            rightsInt,
 		Rights:              s.courses,
-		UnkSize:             0,
+		TokenLength:         0,
 	}
 	s.QueueSendMHFNonBlocking(update)
 }