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/modules/voice-recording/screenShareController.ts

@@ -207,11 +207,13 @@ export class ScreenShareController {
         frameRate: 30,
         bitrateVideo: 2500,
         bitrateVideoMax: 4000,
-        // Video-only GoLive: the -f h264 output muxer cannot carry audio
-        // ("h264 muxer does not support any stream of type audio" → header
-        // write fails → empty stdout → demux 'Invalid data' → black tile).
-        // Audio is not delivered by the GoLive demux path anyway.
-        includeAudio: false,
+        // GoLive with audio: the encoder muxes to NUT (video h264 + opus
+        // audio) so the audio SSRC carries RTP too. Discord's GoLive
+        // pipeline expects audio — a video-only stream shows a static
+        // tile/thumbnail instead of live video. When the source has no
+        // audio track, the encoder's `-map 0:a:0?` yields no audio stream
+        // and the demuxer simply reports none (video still flows).
+        includeAudio: true,
         videoCodec: normalizeVideoCodec("H264"),
       });
       const { command } = prepared;