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>

src/jarvis/tools/base.py

@@ -111,6 +111,14 @@ class Tool(ABC):
         This method creates the context and calls the tool's run method.
         Tools should implement run(), not this method.
         """
+        # Live broadcast state for this turn is carried in request-scoped
+        # thread-local state (set by the bridge) rather than threaded through
+        # the whole engine call chain. Absent (eval / unit test) -> None.
+        try:
+            from jarvis.reply.turn_state import get_broadcasting
+            broadcasting = get_broadcasting()
+        except Exception:
+            broadcasting = None
         context = ToolContext(
             db=db,
             cfg=cfg,
@@ -120,5 +128,6 @@ class Tool(ABC):
             max_retries=max_retries,
             user_print=user_print,
             language=language,
+            broadcasting=broadcasting,
         )
         return self.run(tool_args, context)