docs: Add production deployment guide

[rexlunae]

Comprehensive deployment guide for RustyClaw production use.

Contents

• Quick Start — Installation via setup script or cargo
• Deployment Options — TUI, Gateway daemon, Systemd, Docker
• Configuration — config.toml reference with all key settings
• Secrets Management — Vault usage and security policies
• Monitoring — Health endpoints, logging, observability events
• Security Checklist — Production hardening steps
• Scaling — Single instance vs multi-instance considerations
• Troubleshooting — Common issues and solutions
• Platform Notes — Linux/macOS/ARM specifics

Also updates README.md to link deployment guide and other docs.

[rexlunae]

Excellent deployment guide! 🚢

Comprehensive coverage:

• All deployment modes (TUI, daemon, systemd, Docker)
• Config reference with real examples
• Security checklist is a nice touch
• Good troubleshooting section

One minor nit: the config example shows config.toml but OpenClaw uses config.json — might want to clarify if RustyClaw is switching to TOML or keep it consistent.

Otherwise LGTM. This closes the docs gap for ship-readiness.