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/stream/index.ts

@@ -8,11 +8,26 @@
  */
 import type { AppConfig } from "../config.ts";
 
+/** A live voice session to reuse for single-account Go-Live: the conversation's
+ *  own selfbot client + its negotiated voice session_id. The Go-Live stream is
+ *  created on THIS session (no second login / voice join), so one account both
+ *  hears/speaks (via @discordjs/voice) and broadcasts (via @dank074). */
+export interface SharedVoiceSession {
+  client: unknown;
+  guildId: string;
+  channelId: string;
+  sessionId: string;
+  botId: string;
+}
+
 export interface StreamContext {
   guildId: string;
   voiceChannelId: string;
   /** Post an image to the invoking text channel (used by the screenshot backend). */
   postImage?: (png: Buffer, name: string) => Promise<void>;
+  /** If present and it returns a session, the selfbot backend broadcasts on the
+   *  conversation's existing session instead of a second login (single account). */
+  getSharedSession?: () => SharedVoiceSession | null;
 }
 
 export interface ScreenStreamer {