Replaces the NestJS mana-notify service with a Go implementation.
Features: 4 notification channels (email/SMTP, Expo push, Matrix,
webhook), goroutine worker pool with retry/backoff (replaces BullMQ),
Go template engine (replaces Handlebars), PostgreSQL with auto-migrations
(5 tables), user preferences with quiet hours, idempotency via
externalId, batch sending, scheduled delivery, JWT + service key auth.
22 API endpoints, 1:1 compatible. Binary: 21 MB.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
