fix(channelserver): handle silently swallowed DB scan and exec errors

Several handlers discarded errors from rows.Scan() and db.Exec(),
masking data corruption or connection issues. Scan failures in diva
schedule, event quests, and trend weapons are now logged or returned.
InitializeWarehouse now surfaces its insert error to the caller.

server/channelserver/handlers_diva.go

@@ -84,7 +84,9 @@ func handleMsgMhfGetUdSchedule(s *Session, p mhfpacket.MHFPacket) {
 	} else {
 		defer func() { _ = rows.Close() }()
 		for rows.Next() {
-			_ = rows.Scan(&id, &start)
+			if err := rows.Scan(&id, &start); err != nil {
+				s.logger.Error("Failed to scan diva schedule row", zap.Error(err))
+			}
 		}
 	}