docs(openclaw): add detailed install, secure setup & validation guide
7-phase step-by-step guide:
- Phase 1: Install (Node.js, OpenClaw, onboarding wizard)
- Phase 2: Secure the Gateway (config hardening, password, permissions)
- Phase 3: Connect Channels (WhatsApp, Telegram, Discord, Slack, WebChat)
- Phase 4: Harden the Host (Windows Firewall, WSL2, macOS, router)
- Phase 5: Remote Access (Tailscale Serve setup)
- Phase 6: Validate Security (run validate-security.sh)
- Phase 7: Daemon & Auto-Start (launchd/systemd)
Plus: 22-point verification checklist, maintenance schedule,
emergency procedures, and quick reference card