Add unauthenticated /healthz and /health endpoints for load balancer probes.
Returns {"status":"ok"} with HTTP 200 when the gateway is running.
Also adds documentation for:
- Cloudflare Tunnel as an alternative to Tailscale for secure gateway exposure
- Health check endpoint usage for K8s, AWS ALB, and Cloudflare monitoring
Closes#1971
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
