Add sunbeam check verb with service-level health probes
11 checks across 7 namespaces: gitea version+auth, postgres CNPG
readiness, valkey PONG, openbao sealed state, seaweedfs filer,
kratos health, hydra OIDC discovery, people HTTP (catches 502s),
people API, and livekit. Supports ns and ns/svc scoping.
- checks.py: new module with _http_get (no-redirect opener + mkcert SSL),
kube_exec-based exec checks, and cmd_check dispatch
- kube.py: add kube_exec() and get_domain() (reads from cluster configmap)
- cli.py: add 'check [target]' verb
- 103 tests, all passing