feat: add email notification system (Brevo SMTP + N8N daily digest)

- Add core notification service: types, email-service (nodemailer/Brevo SMTP), notification-service (digest builder, preference CRUD, HTML renderer)
- Add API routes: POST /api/notifications/digest (N8N cron, Bearer auth), GET/PUT /api/notifications/preferences (session auth)
- Add NotificationPreferences UI component (Bell button + dialog with per-type toggles) in Registratura toolbar
- Add 7 Brevo SMTP env vars to docker-compose.yml
- Update CLAUDE.md, ROADMAP.md, DATA-MODEL.md, SYSTEM-ARCHITECTURE.md, CONFIGURATION.md, DOCKER-DEPLOYMENT.md

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/core/notifications/index.ts

@@ -0,0 +1,17 @@
+export type {
+  NotificationType,
+  NotificationTypeInfo,
+  NotificationPreference,
+  DigestSection,
+  DigestItem,
+  DigestResult,
+  EmailPayload,
+} from "./types";
+export { NOTIFICATION_TYPES, defaultPreference } from "./types";
+export { sendEmail } from "./email-service";
+export {
+  getPreference,
+  savePreference,
+  getAllPreferences,
+  runDigest,
+} from "./notification-service";