When nginx is stopped (e.g. during traefik/caddy tests), the
post-create trigger should not attempt to build and reload the
nginx config as the service is not running.
The post-create trigger was not executable so plugn skipped it.
Also skip generating the 502 config when PROXY_PORT_MAP is empty
(e.g. after ports:clear) to avoid a sigil template index error.
When an app has no web listeners (not yet deployed, no web process type,
or web processes not running), generate a minimal nginx config that
returns 502 Bad Gateway instead of having no config at all. This ensures
domains resolve, monitoring tools detect non-200 status codes, and SSL
certificate provisioning tools like letsencrypt can function.