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/protocol/wave.go

@@ -0,0 +1,80 @@
+// Package protocol implements the obs-teleport wire format.
+//
+// This file builds the audio ("WAVE") side of the protocol: Header +
+// WaveHeader + raw interleaved PCM, byte-for-byte compatible with the
+// reference implementation (GPL-2.0).
+package protocol
+
+// BuildWavePacket assembles a complete ""WAVE"" wire packet:
+// Header + WaveHeader + interleaved PCM payload.
+//
+// pcm is already interleaved (L,R,L,R,… for stereo). format must be one of
+// the AudioFormat* constants. frames is the PCM frame count (samples per
+// channel). The returned slice is a freshly allocated buffer safe to hand to
+// the network.
+func BuildWavePacket(timestamp uint64, format int32, sampleRate, speakers, frames int32, pcm []byte) ([]byte, error) {
+	expected := int64(speakers) * int64(frames) * int64(bytesPerSample(format))
+	if int64(len(pcm)) != expected {
+		return nil, errBadPCMLength{got: len(pcm), want: int(expected)}
+	}
+
+	h := Header{
+		Type:      AudioType,
+		Timestamp: timestamp,
+		Size:      int32(len(pcm)),
+	}
+	wave := WaveHeader{
+		Format:     format,
+		SampleRate: sampleRate,
+		Speakers:   speakers,
+		Frames:     frames,
+	}
+	return WritePacket(h, nil, &wave, pcm)
+}
+
+// bytesPerSample maps an AudioFormat* value to its size in bytes.
+func bytesPerSample(format int32) int {
+	switch format {
+	case AudioFormatU8:
+		return 1
+	case AudioFormatS16:
+		return 2
+	case AudioFormatS32, AudioFormatF32:
+		return 4
+	default:
+		return 0
+	}
+}
+
+// errBadPCMLength is returned when pcm length does not match the declared
+// format/speakers/frames.
+type errBadPCMLength struct{ got, want int }
+
+func (e errBadPCMLength) Error() string {
+	return "protocol: pcm length mismatch" +
+		": got " + itoa(e.got) + " bytes, want " + itoa(e.want)
+}
+
+// itoa is a tiny local int→string helper to avoid importing strconv in the
+// hot path callers.
+func itoa(v int) string {
+	if v == 0 {
+		return "0"
+	}
+	neg := v < 0
+	if neg {
+		v = -v
+	}
+	var buf [20]byte
+	i := len(buf)
+	for v > 0 {
+		i--
+		buf[i] = byte('0' + v%10)
+		v /= 10
+	}
+	if neg {
+		i--
+		buf[i] = '-'
+	}
+	return string(buf[i:])
+}