Surfaces the DNS/Cloudflare/public state that previously required editing
castle.yaml + curl:
- API: GET /gateway now returns domain, public_domain, tunnel_id,
tunnel_connected, and a public_url per public route; new PUT /gateway/config
edits tls/domain/public_domain/tunnel_id in castle.yaml (deploy to apply).
save_config now persists public_domain/tunnel_id (previously dropped).
- UI: a GatewaySettings row in the Gateway panel shows TLS / domain / public
(tunnel up/down + public_domain) with inline edit; each public route gets a
green "public" badge linking to its <name>.<public_domain> URL.