fix: replace fmt.Sprintf in logger calls with structured fields and add LoopDelay default

fmt.Sprintf inside zap logger calls defeats structured logging,
making log aggregation and filtering harder. All 6 sites now use
proper zap fields (zap.Uint32, zap.Uint8, zap.String).

LoopDelay had no viper.SetDefault, so omitting it from config.json
caused a zero-value (0 ms) busy-loop in the recv loop. Default is
now 50 ms, matching config.example.json.

server/channelserver/handlers_session.go

@@ -58,7 +58,7 @@ func handleMsgSysLogin(s *Session, p mhfpacket.MHFPacket) {
 	if !s.server.erupeConfig.DebugOptions.DisableTokenCheck {
 		if err := s.server.sessionRepo.ValidateLoginToken(pkt.LoginTokenString, pkt.LoginTokenNumber, pkt.CharID0); err != nil {
 			_ = s.rawConn.Close()
-			s.logger.Warn(fmt.Sprintf("Invalid login token, offending CID: (%d)", pkt.CharID0))
+			s.logger.Warn("Invalid login token", zap.Uint32("charID", pkt.CharID0))
 			return
 		}
 	}