feat: implement M1 teleport protocol sender

Stream a synthetic test pattern and silent PCM audio over the OBS
Teleport protocol:
- protocol: wire format (Header/ImageHeader/WaveHeader), BT.709 full
  range colour matrix, JPEG encode via turbojpeg cgo, WAVE packet builder
- output: TCP sender with per-connection buffered channels and drop-on-overflow
- discovery: multicast announce via peerdiscovery
- cmd: teleportfling CLI with flags, test-pattern frame generator

Verified end-to-end: OBS discovers and renders the stream with correct
colours and motion.

internal/output/sender_test.go

@@ -0,0 +1,61 @@
+package output
+
+import (
+	"io"
+	"net"
+	"testing"
+	"time"
+)
+
+// TestSendReceive does an end-to-end round trip: a TCP client connects to
+// the Sender, Send broadcasts a frame, and the client must read it back.
+func TestSendReceive(t *testing.T) {
+	s := New()
+	port, err := s.Listen("127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("Listen: %v", err)
+	}
+
+	conn, err := net.Dial("tcp", "127.0.0.1:"+itoa(port))
+	if err != nil {
+		t.Fatalf("Dial: %v", err)
+	}
+	defer func() { _ = conn.Close() }()
+	defer func() { _ = conn.(*net.TCPConn).SetLinger(0) }()
+
+	// Give the accept loop a moment to register the connection.
+	deadline := time.Now().Add(2 * time.Second)
+	for s.NumConns() == 0 && time.Now().Before(deadline) {
+		time.Sleep(5 * time.Millisecond)
+	}
+	if s.NumConns() != 1 {
+		t.Fatalf("NumConns = %d, want 1", s.NumConns())
+	}
+
+	payload := []byte("frame-one")
+	s.Send(payload)
+
+	got := make([]byte, len(payload))
+	if _, err := io.ReadFull(conn, got); err != nil {
+		t.Fatalf("read: %v", err)
+	}
+	if string(got) != "frame-one" {
+		t.Errorf("round trip mismatch: got %q", got)
+	}
+
+	s.Close()
+}
+
+func itoa(v int) string {
+	if v == 0 {
+		return "0"
+	}
+	var buf [20]byte
+	i := len(buf)
+	for v > 0 {
+		i--
+		buf[i] = byte('0' + v%10)
+		v /= 10
+	}
+	return string(buf[i:])
+}