feat(selfbot): broadcast desktop audio + smart subtitles in the browse scenario

Two broadcast-experience improvements:

- Audio: the Go-Live stream was video-only. Capture the desktop sound (the
  default PipeWire/Pulse sink monitor, @DEFAULT_MONITOR@) as a second ffmpeg
  input and mux AAC into the mpegts; the library re-encodes it to Opus for
  Discord. Controlled by STREAM_AUDIO / STREAM_AUDIO_SOURCE (default on). ffmpeg
  inherits XDG_RUNTIME_DIR to reach the pulse socket. Verified: the streamer now
  reports "Found audio stream" and the monitor carries Chrome audio (~-11 dB).
- Subtitles: in the browse scenario, default captions OFF, but auto-enable a
  Korean track when the video offers one (getOption captions tracklist ->
  setOption / unloadModule).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

bot/src/config.ts

@@ -42,6 +42,11 @@ export const config = {
   selfbotToken: opt("DISCORD_SELFBOT_TOKEN"),
   // Use NVENC hardware encode + hw-accelerated decode for the stream (RTX 5050).
   streamHw: opt("STREAM_HW", "1") !== "0",
+  // Capture desktop audio into the broadcast so the stream has sound. Pulls the
+  // PipeWire/Pulse monitor of the default sink (what the desktop plays). Set
+  // STREAM_AUDIO=0 to mute; STREAM_AUDIO_SOURCE overrides the capture source.
+  streamAudio: opt("STREAM_AUDIO", "1") !== "0",
+  streamAudioSource: opt("STREAM_AUDIO_SOURCE", "@DEFAULT_MONITOR@"),
 
   // novnc backend
   novncUrl: opt("NOVNC_URL", ""),