feat(stream): single-account Go-Live — broadcast on the conversation's session

Proven approach: the conversation (hear+speak) runs on @discordjs/voice; the
Go-Live broadcast is a SEPARATE stream connection created on the SAME selfbot
session (exactly like a real Discord client), so ONE account hears, speaks, AND
broadcasts — no second login, no self_deaf, no voice conflict.

- voice.ts captures its own voice session_id (adapter wrap) and exposes
  getSharedSession() {client, guildId, channelId, sessionId, botId}.
- broadcast.ts threads it into the StreamContext.
- selfbot.ts: when a shared session is present, build the Streamer on the
  conversation client and create the stream on its session_id (no login/joinVoice/
  humanPause); teardown only stops the stream (never leaves voice/destroys the
  shared client). Falls back to the dedicated-account path otherwise.

Verified live: Go-Live connected in ~7s while the conversation voice stayed
ready, and the broadcast was visible in Discord — all on one account.

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

bot/src/broadcast.ts

@@ -31,7 +31,10 @@ export function peekStreamer(guildId: string): ScreenStreamer | undefined {
   return streamers.get(guildId);
 }
 
-type BroadcastSession = Pick<VoiceSession, "getBroadcasting" | "onBroadcastAction">;
+type BroadcastSession = Pick<
+  VoiceSession,
+  "getBroadcasting" | "onBroadcastAction" | "getSharedSession"
+>;
 
 /**
  * Wire a voice session to a streamer (no auto-start). Pure (no config / registry
@@ -107,8 +110,14 @@ export async function maybeCoupleBroadcast(
 ): Promise<void> {
   if (!config.screenBrowser) return;
   const streamer = await getStreamer(ctx.guildId);
-  wireBroadcast(session, streamer, ctx);
-  void autoStartBroadcast(streamer, ctx);
+  // Let the selfbot backend broadcast on the conversation's own session
+  // (single-account Go-Live) instead of a second login.
+  const ctxWithSession: StreamContext = {
+    ...ctx,
+    getSharedSession: () => session.getSharedSession?.() ?? null,
+  };
+  wireBroadcast(session, streamer, ctxWithSession);
+  void autoStartBroadcast(streamer, ctxWithSession);
 }
 
 /** Stop the broadcast for a guild if one is live (e.g. on leave). */