feat(box): add --standalone-box flag and 3-way transport decision for Box runtime

Align Box runtime connection logic with Plugin runtime's pattern:
- Docker: WebSocket to langbot_box container (ws://langbot_box:5411)
- --standalone-box: WebSocket to external Box process (ws://localhost:5411)
- Windows: subprocess + WebSocket (workaround for async stdio limitation)
- Unix/macOS: subprocess + stdio pipe (unchanged)

BoxRuntimeConnector now inherits ManagedRuntimeConnector for subprocess
lifecycle reuse. Add langbot_box service to docker-compose.yaml.

docker/docker-compose.yaml

@@ -18,16 +18,28 @@ services:
     networks:
       - langbot_network
 
+  langbot_box:
+    image: rockchin/langbot:latest
+    container_name: langbot_box
+    volumes:
+      - ./data/box:/workspaces
+      # Mount container runtime socket for Box sandbox backend.
+      # Uncomment the one that matches your container runtime:
+      # - /var/run/podman/podman.sock:/var/run/podman/podman.sock   # Podman
+      - /var/run/docker.sock:/var/run/docker.sock                   # Docker
+    restart: on-failure
+    environment:
+      - TZ=Asia/Shanghai
+    command: ["uv", "run", "--no-sync", "-m", "langbot_plugin.box", "--mode", "ws"]
+    networks:
+      - langbot_network
+
   langbot:
     image: rockchin/langbot:latest
     container_name: langbot
     volumes:
       - ./data:/app/data
       - ./data/box:/workspaces
-      # Mount container runtime socket for Box sandbox (Docker backend).
-      # Uncomment the one that matches your container runtime:
-      # - /var/run/podman/podman.sock:/var/run/podman/podman.sock   # Podman
-      - /var/run/docker.sock:/var/run/docker.sock                   # Docker
     restart: on-failure
     environment:
       - TZ=Asia/Shanghai