fix(deploy): proxy /deepflow-backend/* to backend /api/* in Docker + expose deepflow ports

- next.config.js: server-side rewrites so the standalone frontend (built with
  NEXT_PUBLIC_API_URL=/deepflow-backend) can reach deepflow-backend:8000/api/*
  without CORS; target overridable via DEEPFLOW_BACKEND_HOST
- docker-compose: expose deepflow-frontend 3001:3000 and deepflow-backend 8000:8000

deployment/docker/deepdata/docker-compose.yml

@@ -205,6 +205,8 @@ services:
     container_name: deepflow-backend
     env_file:
       - .env
+    ports:
+      - "8000:8000"
     volumes:
       - ./conf.yaml:/app/conf.yaml:ro
       - deepflow-log-volume:/var/log/deepflow
@@ -219,6 +221,8 @@ services:
     container_name: deepflow-frontend
     env_file:
       - .env
+    ports:
+      - "3001:3000"
     depends_on:
       - deepflow-backend
     restart: on-failure