Add sACN input/output support and fix multi-source merging

- Add sACN/E1.31 protocol support for both input and output
- from_proto = "sacn" to receive from sACN multicast
- proto = "sacn" to output via sACN multicast
- Fix remap engine to maintain persistent state per output universe
- Multiple inputs targeting same output now merge correctly
- Prevents flickering when multiple universes feed same output

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

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

sacn/sender.go

@@ -0,0 +1,67 @@
+package sacn
+
+import (
+	"crypto/rand"
+	"net"
+	"sync"
+)
+
+// Sender sends sACN (E1.31) packets
+type Sender struct {
+	conn       *net.UDPConn
+	sourceName string
+	cid        [16]byte
+	sequences  map[uint16]uint8
+	seqMu      sync.Mutex
+}
+
+// NewSender creates a new sACN sender
+func NewSender(sourceName string) (*Sender, error) {
+	conn, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4zero, Port: 0})
+	if err != nil {
+		return nil, err
+	}
+
+	// Generate random CID
+	var cid [16]byte
+	rand.Read(cid[:])
+
+	return &Sender{
+		conn:       conn,
+		sourceName: sourceName,
+		cid:        cid,
+		sequences:  make(map[uint16]uint8),
+	}, nil
+}
+
+// SendDMX sends DMX data to a universe via multicast
+func (s *Sender) SendDMX(universe uint16, data []byte) error {
+	s.seqMu.Lock()
+	seq := s.sequences[universe]
+	s.sequences[universe] = seq + 1
+	s.seqMu.Unlock()
+
+	pkt := BuildDataPacket(universe, seq, s.sourceName, s.cid, data)
+	addr := MulticastAddr(universe)
+
+	_, err := s.conn.WriteToUDP(pkt, addr)
+	return err
+}
+
+// SendDMXUnicast sends DMX data to a specific address
+func (s *Sender) SendDMXUnicast(addr *net.UDPAddr, universe uint16, data []byte) error {
+	s.seqMu.Lock()
+	seq := s.sequences[universe]
+	s.sequences[universe] = seq + 1
+	s.seqMu.Unlock()
+
+	pkt := BuildDataPacket(universe, seq, s.sourceName, s.cid, data)
+
+	_, err := s.conn.WriteToUDP(pkt, addr)
+	return err
+}
+
+// Close closes the sender
+func (s *Sender) Close() error {
+	return s.conn.Close()
+}