feat(collector): brain event 중계 추가 — Watcher 이벤트를 Gateway로 전달

- collector.py: _forward_events_loop — BrainEvent를 JSON으로 serialize하여 /api/event POST
- gateway.py: /api/event 엔드포인트 — 수신한 이벤트를 bot event_queue에 주입
- main.py: event_queue를 CollectorBridge에 전달

이제 task.md, implementation_plan, walkthrough 변경사항이 Collector→Gateway→Discord 경로로 전달됨

main.py

@@ -65,7 +65,8 @@ async def main():
         local.ensure_dirs()
         remote = RemoteTransport(Config.REMOTE_BRIDGE_URL, api_key=Config.GATEWAY_API_KEY)
 
-        collector = CollectorBridge(local, remote, project_name=Config.PROJECT_NAME)
+        collector = CollectorBridge(local, remote, project_name=Config.PROJECT_NAME,
+                                    event_queue=event_queue)
         logger.info(f"Collector mode: {Config.REMOTE_BRIDGE_URL}")
 
         # Optionally start watcher for brain events (local display only)