Bundled Chimeway.Notifier implementation for Accrue dunning notifications.
Resolves Accrue domain models (Subscription → Customer) to produce
email-channel recipient maps. Phase 98-capable Chimeway receives a stable opaque
recipient reference plus transient user:<email> delivery identity; Chimeway 1.0
receives its legacy email identity. Implements required callbacks plus
channels/2 (email-only), orchestration/2 (:immediate), workflow/2
(48h escalation per SEED-003), and rendering/2 (email render keys).