docs(integrations): add OpenClaw integration guide (en + zh)

[GongHening]

Summary

• Add OpenClaw integration guide — run OpenClaw Gateway inside a Cube MicroVM for kernel-level agent isolation
• Both English (docs/guide/integrations/openclaw.md) and Chinese (docs/zh/guide/integrations/openclaw.md) versions included
• Updated the published articles table in both language index pages

What the guide covers

1. Setup — Cube deployment, template creation (2G writable layer), environment variables
2. Integration diff — native openclaw gateway vs. Sandbox.create() with side-by-side code comparison
3. Runnable demo — full run_openclaw.py script that installs Node.js 24, configures OpenClaw, starts the gateway, and runs a
   health-check loop
4. Going further — network isolation, timeouts, host directory mounts, pause/resume, pre-built custom image

Key lessons baked in

The guide is based on a real end-to-end deployment and captures non-obvious details:

• Correct config sequence: minimal JSON → openclaw doctor --fix → --bind loopback --allow-unconfigured
• Reliable process checking (pgrep -x / grep -v grep instead of bare ps aux | grep)
• Startup script wrapper to avoid SDK timeouts on nohup commands
• Template version must match CubeSandbox code version
• --writable-layer-size 2G requirement for Node.js + OpenClaw