Add a notification

A notification is a template in apps/notifications, queued as a job. Its category decides which channels it may use and whether users can turn it off.

1. Payload. Add a z.object({ template: z.literal("<area>.<name>"), to, data }) to notificationPayload in packages/jobs/src/queues.ts and pick its queue in notificationQueue (notifications-critical only for codes, security and billing). to is { userId }, { email, locale } or { orgId, roles }.
2. Copy. Every string in packages/i18n/messages/*.json, every locale: email.<camelCaseName>, notification.<area>.<name>.title and .body (push and in-app), sms.<camelCaseName>. Compare todo.reminder: email.todoReminder, notification.todo.reminder.
3. Email. A component in packages/email/src/templates/ with its subject, exported from packages/email/src/index.ts, and a preview in packages/email/src/previews/ (bun run --cwd packages/email dev serves them on http://localhost:3030).
4. In-app. Its data schema in inAppNotifications in packages/contracts/src/notifications.ts, so apps can render it.
5. Template. An entry in templates in apps/notifications/src/dispatch/templates.ts with its category and a renderer per channel it uses (email, inApp, push, sms). The satisfies clause fails check-types until it exists.
6. Category. Reuse one from notificationCategories in packages/contracts/src/notifications.ts. A new one gets its default channels there and a title and description under notificationSettings.categories.<name>. mutable: false means users can't turn it off.
7. Trigger. From a service: a producer for the queue and add("send", payload, { jobId }). From a domain event: route the event to events-notifications in eventSubscribers and map it in apps/notifications/src/events/events.processor.ts.
8. Tests. bun run test (i18n completeness, email rendering in packages/email/src/render.test.tsx), then bun run test:integration (apps/notifications/test/notifications.integration.test.ts sends through Mailpit and the fake push and SMS servers).
9. Finish. The verify skill, then the i18n-checker agent on the new copy and the reviewer agent on the change (delivery through DeliveryLog.claim(), preferences, the category's mutable flag).