Resolves the six open questions: host-level forward-retry config,
Notify.Status returns a status record, 10-min stuck threshold, a
site-local Forwarding state, site-side logging of forward failures
only, and point-in-time KPIs computed from the Notifications table.
Captures the basic design for a reliable notification outbox: sites
store-and-forward notifications to the central cluster, which logs
them to a type-agnostic Notifications table (single audit source) and
delivers them via per-type adapters with retry, parking, and KPIs.
