refactor: 合并 celery-beat 到 celery-worker (4→3容器)

celery-worker 加 -B 参数启动嵌入式 Beat，省去独立 celery-beat 容器。
定时任务由代码中 beat_schedule 驱动，schedule 文件保持持久化。

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

docker-compose.yml

@@ -17,7 +17,7 @@ services:
 
   celery-worker:
     build: ./backend
-    command: celery -A celery_worker.celery_app worker --loglevel=info -Q h3c_onu_ms
+    command: celery -A celery_worker.celery_app worker -B --loglevel=info -Q h3c_onu_ms --schedule=/tmp/celerybeat-schedule
     env_file:
       - ./backend/.env
     volumes:
@@ -27,16 +27,6 @@ services:
       backend:
         condition: service_healthy
 
-  celery-beat:
-    build: ./backend
-    command: celery -A celery_worker.celery_app beat --loglevel=info --schedule=/tmp/celerybeat-schedule
-    env_file:
-      - ./backend/.env
-    restart: unless-stopped
-    depends_on:
-      backend:
-        condition: service_healthy
-
   frontend:
     build: ./frontend
     ports: