Initial implementation of ArtNet remapping proxy

Channel-level DMX remapping between ArtNet universes with:
- TOML configuration with multiple address formats (net.subnet.universe, plain number)
- ArtPoll discovery for output nodes
- Configurable channel ranges for fixture spillover handling

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

artnet/sender.go

@@ -0,0 +1,92 @@
+package artnet
+
+import (
+	"net"
+	"sync"
+)
+
+// Sender sends ArtNet packets
+type Sender struct {
+	conn          *net.UDPConn
+	broadcastAddr *net.UDPAddr
+	sequences     map[Universe]uint8
+	seqMu         sync.Mutex
+}
+
+// NewSender creates a new ArtNet sender
+func NewSender(broadcastAddr string) (*Sender, error) {
+	// Create a UDP socket for sending
+	conn, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4zero, Port: 0})
+	if err != nil {
+		return nil, err
+	}
+
+	// Enable broadcast
+	if err := conn.SetWriteBuffer(65536); err != nil {
+		conn.Close()
+		return nil, err
+	}
+
+	broadcast, err := net.ResolveUDPAddr("udp4", broadcastAddr+":"+string(rune(Port)))
+	if err != nil {
+		// Try parsing as IP:Port
+		broadcast, err = net.ResolveUDPAddr("udp4", broadcastAddr)
+		if err != nil {
+			broadcast = &net.UDPAddr{
+				IP:   net.ParseIP(broadcastAddr),
+				Port: Port,
+			}
+		}
+	}
+
+	return &Sender{
+		conn:          conn,
+		broadcastAddr: broadcast,
+		sequences:     make(map[Universe]uint8),
+	}, nil
+}
+
+// SendDMX sends a DMX packet to a specific address
+func (s *Sender) SendDMX(addr *net.UDPAddr, universe Universe, data []byte) error {
+	s.seqMu.Lock()
+	seq := s.sequences[universe]
+	seq++
+	if seq == 0 {
+		seq = 1 // Skip 0
+	}
+	s.sequences[universe] = seq
+	s.seqMu.Unlock()
+
+	pkt := BuildDMXPacket(universe, seq, data)
+	_, err := s.conn.WriteToUDP(pkt, addr)
+	return err
+}
+
+// SendDMXBroadcast sends a DMX packet to the broadcast address
+func (s *Sender) SendDMXBroadcast(universe Universe, data []byte) error {
+	return s.SendDMX(s.broadcastAddr, universe, data)
+}
+
+// SendPoll sends an ArtPoll packet to the broadcast address
+func (s *Sender) SendPoll() error {
+	pkt := BuildPollPacket()
+	_, err := s.conn.WriteToUDP(pkt, s.broadcastAddr)
+	return err
+}
+
+// SendPollReply sends an ArtPollReply to a specific address
+func (s *Sender) SendPollReply(addr *net.UDPAddr, localIP [4]byte, shortName, longName string, universes []Universe) error {
+	pkt := BuildPollReplyPacket(localIP, shortName, longName, universes)
+	_, err := s.conn.WriteToUDP(pkt, addr)
+	return err
+}
+
+// Close closes the sender
+func (s *Sender) Close() error {
+	return s.conn.Close()
+}
+
+// BroadcastAddr returns the configured broadcast address
+func (s *Sender) BroadcastAddr() *net.UDPAddr {
+	return s.broadcastAddr
+}