app-heartbeat

The ONE app-agnostic APP-ALIVE contract for the nordisk Build Thing: a serde manifest any deployable app declares (identity + liveness markers + the functions/capabilities it exposes), plus a pure evaluator (`HeartbeatProbe`) that reads the manifest and a deployment's observed output and returns a per-function verdict + overall liveness. NOT app-specific — korp is only the reference implementer; the probe never hardcodes any app. Consumed by the dwarves ⚒ Build Thing (one robot UI test per declared function) and by Skidbladnir sockets (a `Probe`). Dep-light: serde only.