atecontroller metrics are never scraped

atecontroller is the only control plane component with no Prometheus target. It uses
`InitMetricsPushOnly` (`cmd/atecontroller/main.go:112`) and its pod carries no `prometheus.io`
annotations, so the manager's `:8080` is never scraped, while ateapi, atelet and atenet-router
serve `/metrics` on 9090 and are. `docs/observability.md:178` assumes every component is scraped.

Should atecontroller move to the `InitMetrics` plus `StartMetricsServer` shape on 9090, or is
push-only intended, in which case the dead `:8080` port should go instead?