fix(gateway): deliver audio + per-IDR SPS/PPS in GoLive screen share

Screen share showed a single frozen frame: the GoLive pipeline sent video
only (-"-an", h264 muxer cannot carry audio) so the audio SSRC never
transmitted and Discord kept the stream in thumbnail state.

- prepareStream: mux NUT when includeAudio (h264 muxer drops audio) and
  return the actual container format
- Demuxer: support NUT input with a second output pipe (fd3) carrying
  Ogg Opus; parse OGG pages into opus frames (20ms, 48kHz) emitted as
  GoLiveFrames; fix metadata parsing that dropped the audio stream line
  when it arrived in a later stderr chunk (early parsedMeta return)
- playStream: pipe audio.stream into AudioStream → RTP on the audio SSRC
- Encoders: -x264-params repeat-headers=1 → SPS/PPS inline before EVERY
  IDR (NUT remux drops container extradata; also enables PLI recovery)
- screenShareController: includeAudio true
- tests: demuxerNut.test.ts — OGG parser unit test + real ffmpeg NUT
  integration (video access units + parsed opus frames)

services/discord-gateway/src/goLive/WebRtcWrapper.ts

@@ -179,6 +179,9 @@ export class WebRtcConnWrapper {
       throw new Error("WebRTC connection not ready");
     }
     const { audioSsrc, videoSsrc } = this.mediaConnection.webRtcParams;
+    console.log(
+      `[goLive:WebRtc] setPacketizer(${videoCodec}) audioSsrc=${audioSsrc} videoSsrc=${videoSsrc} rtxSsrc=${this.mediaConnection.webRtcParams.rtxSsrc}`,
+    );
     this._videoCodec = normalizeVideoCodec(videoCodec);
     // Audio packetizer: opus 120 @ 48kHz, playout delay ext id 5 (like @dank074)
     this._audioTrack?.setPacketizer(