Swap the notification template source

• Interface: TemplateSource (abstract class, bind(payload): Promise<BoundTemplate>) in apps/notifications/src/dispatch/templates.ts.
• Today: CodeTemplateSource: the templates registry in the same file, rendering React Email components from packages/email with copy from packages/i18n.
• Bound in: apps/notifications/src/dispatch/notifications.module.ts ({ provide: TemplateSource, useClass: CodeTemplateSource }).
• Env: none today.

Swap

1. Store templates (db-change skill; the notifications schema is the service's own).
2. Implement TemplateSource: look up the stored template for payload.template (and the organization, for branding), cache it in Redis, and return a BoundTemplate that renders it. Fall back to CodeTemplateSource when no stored version exists, so every template keeps working.
3. Bind the new class in notifications.module.ts. The dispatcher and the email channel don't change.
4. Validate stored content before rendering: the fields it may use are the template's payload schema in packages/jobs/src/queues.ts.

Tests

apps/notifications/test/notifications.integration.test.ts sends through Mailpit; add cases for a stored template and for the fallback. packages/email/src/render.test.tsx covers the code templates.

Finish

1. The verify skill.
2. Ask the reviewer agent to review the change, and the security-reviewer agent: a new implementation brings its own credentials and sends data somewhere new. If you wrote a migration, the migration-reviewer agent too.
3. Update the seam's row in the README's "Scaling path" table if what's "Now" changed.