Update 0.5.5.65

Callback service lifecycle, health tests, and documentation

The callback-only Docker service now starts with the normal Compose stack; the callback profile is no longer required.
Added CALLBACK_BIND_IP so deployments can bind the callback listener to loopback, a selected host interface, or explicitly all interfaces.
Added separate internal and public callback health checks in the GUI with tested URL, HTTP status, response time, and reachability result.
The internal test validates Docker service networking; the public test validates the configured FQDN/reverse-proxy path.
Updated installation, security, README, environment example, and callback deployment documentation.
Reworded the repository warning about .env and runtime data as normal deployment/security guidance rather than a development note.