relay: fix buffer leak on UDP read error by returning buffer to pool

When ReadFromUDP fails in readPackets, the buffer was not returned to the
sync.Pool, causing a small but persistent leak under error conditions.
Return the buffer before continuing to ensure reuse and stable memory.

Scope: minimal hotfix (no broader refactors).

relay/relay.go

@@ -187,6 +187,8 @@ func (s *UDPProxyServer) readPackets() {
 		n, remoteAddr, err := s.conn.ReadFromUDP(buf)
 		if err != nil {
 			logger.Error("Error reading UDP packet: %v", err)
+			// Return buffer to pool on read error to avoid leaks
+			bufferPool.Put(buf[:1500])
 			continue
 		}
 		s.packetChan <- Packet{data: buf[:n], remoteAddr: remoteAddr, n: n}