fix(mpc-system): 为 account-service 添加 RabbitMQ 配置

- 添加 MPC_RABBITMQ_HOST/PORT/USER/PASSWORD 环境变量
- 添加 rabbitmq 到 depends_on

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

backend/mpc-system/docker-compose.yml

@@ -298,6 +298,10 @@ services:
       MPC_REDIS_HOST: redis
       MPC_REDIS_PORT: 6379
       MPC_REDIS_PASSWORD: ${REDIS_PASSWORD:-}
+      MPC_RABBITMQ_HOST: rabbitmq
+      MPC_RABBITMQ_PORT: 5672
+      MPC_RABBITMQ_USER: ${RABBITMQ_USER:-mpc_user}
+      MPC_RABBITMQ_PASSWORD: ${RABBITMQ_PASSWORD:-mpc_rabbit_password}
       MPC_COORDINATOR_URL: session-coordinator:50051
       MPC_JWT_SECRET_KEY: ${JWT_SECRET_KEY}
       # API 认证密钥 (与 mpc-service 配置的 MPC_API_KEY 一致)
@@ -309,6 +313,8 @@ services:
         condition: service_healthy
       redis:
         condition: service_healthy
+      rabbitmq:
+        condition: service_healthy
       session-coordinator:
         condition: service_healthy
     healthcheck: