feat(notification): implement the notification delivery platform

Maps the 31-module plan onto the registry's 19 leaves as packages; the two
edges the registry forbids (provider->httpclient, inbox->messaging) are
replaced by application-owned ports. See docs/notification/module-mapping.md.

Acceptance is not delivery: ProviderSubmissionResult refuses to carry a
delivery outcome, and AMBIGUOUS is a first-class terminal state that blocks
automatic retry and fallback until reconciliation resolves it.

Providers: SES (SigV4 + SNS callback), Twilio (X-Twilio-Signature +
reconciliation), FCM (FID-primary batch), APNs, Web Push (RFC 8030/8291/8292),
SMTP and webhook. Contact points are AES-256-GCM encrypted with a separate
HMAC lookup fingerprint; nothing raw reaches a log, metric tag or exception.

Dispatch commits the attempt row, calls the provider with no transaction open,
then records the outcome; the durable queue uses FOR UPDATE SKIP LOCKED.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/notification/adr/NOTIF-ADR-001-durable-acceptance.md

@@ -0,0 +1,27 @@
+# NOTIF-ADR-001 — `submit()` means durable acceptance
+
+## Status
+
+Accepted.
+
+## Context
+
+The obvious API for a notification platform is `send()` returning success or failure. Every channel
+this platform supports makes that return value a lie:
+
+- SES accepts a request, returns a `MessageId`, and can still decline to send.
+- Twilio separates `accepted`, `sent` and `delivered` into distinct, later events.
+- APNs accepts a notification and may then deliver, store or discard it.
+- Web Push separates push-service acceptance from user-agent acknowledgement at the protocol level.
+
+## Decision
+
+`submit()` and `schedule()` return once the logical request and its recipient jobs are committed to
+the database. The receipt carries `notificationId`, `RequestStatus` and `acceptedAt`, and has no
+`delivered`, `sent` or `read` component. No provider is contacted while the transaction is open.
+
+## Consequences
+
+Callers cannot mistake acceptance for delivery, because the type does not offer that reading.
+Delivery state is a separate query against the projection built from the provider event ledger. The
+cost is that "did it arrive?" is a second question — which is the honest number of questions.