feat: couple broadcast to voice + voice-controlled broadcast toggle

Completes the STREAM_BROWSER=true behaviour:
- handleJoin auto-starts the broadcast on voice join and wires the session to
  the guild streamer; each turn reports the live state to the brain so search
  routes Chrome (live) vs Gemini (off).
- New setBroadcast tool lets the user toggle the broadcast by voice ("방송
  켜줘/꺼줘") via the LLM (no hardcoded phrases); it refuses when
  STREAM_BROWSER=false. The directive flows brain -> bridge (broadcast_action)
  -> bot streamer.start/stop, guarded by isActive() so it's idempotent.
- Per-turn IPC uses a thread-local (reply/turn_state.py) instead of threading
  params through the whole engine chain: bridge sets broadcasting in, tool
  records the directive out; Tool.execute exposes broadcasting on ToolContext.

Bot typecheck clean; brain covered by tests/test_set_broadcast.py (+ existing
routing tests). Specs + docs updated.

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

bot/src/voice.ts

@@ -71,6 +71,11 @@ export class VoiceSession {
   private playQueue: Buffer[] = [];
   /** Optional callback to surface transcripts/replies to a text channel. */
   onTurn?: (info: { user: string; transcript: string; reply: string }) => void;
+  /** Live screen-share state, sent with each turn so the brain routes search
+   *  (Chrome while broadcasting, Gemini when off). */
+  getBroadcasting?: () => boolean;
+  /** Apply a broadcast directive the brain requested (start/stop the stream). */
+  onBroadcastAction?: (action: "start" | "stop") => void | Promise<void>;
 
   constructor(channel: VoiceBasedChannel) {
     this.guildId = channel.guild.id;
@@ -123,10 +128,19 @@ export class VoiceSession {
     const wav = pcm16MonoToWav(mono, DISCORD_RATE);
 
     try {
-      const result = await converse(wav);
+      const result = await converse(wav, this.getBroadcasting?.());
       if (result.transcript) {
         this.onTurn?.({ user: userId, transcript: result.transcript, reply: result.reply });
       }
+      // Apply any broadcast directive the brain requested (e.g. user said
+      // "방송 켜줘 / 꺼줘") before playing the reply.
+      if (result.broadcast_action && this.onBroadcastAction) {
+        try {
+          await this.onBroadcastAction(result.broadcast_action);
+        } catch (e) {
+          console.error("[voice] broadcast action failed:", e);
+        }
+      }
       const audio = decodeWav(result.audio_b64);
       if (audio) this.play(audio);
     } catch (err) {