feat(notifications): add multi-channel notification module with Email, FCM, templates, and event listeners

- Domain: NotificationLog/NotificationPreference entities, repositories, channel value object
- Infrastructure: EmailService (nodemailer/SMTP), FcmService (firebase-admin), TemplateService (Handlebars)
- Application: SendNotification CQRS command, UserRegistered + AgentVerified event listeners
- Presentation: NotificationsController with history, preferences, and templates endpoints
- Prisma: NotificationLog and NotificationPreference models with proper indexes
- Templates: Vietnamese notification templates for user.registered, agent.verified, listing.approved, inquiry.received, password.reset

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/src/modules/notifications/domain/index.ts

@@ -0,0 +1,16 @@
+export type { NotificationEntity, NotificationStatus } from './entities/notification.entity';
+export type { NotificationPreferenceEntity } from './entities/notification-preference.entity';
+export { NotificationSentEvent } from './events/notification-sent.event';
+export {
+  NOTIFICATION_REPOSITORY,
+  type INotificationRepository,
+  type CreateNotificationDto,
+} from './repositories/notification.repository';
+export {
+  NOTIFICATION_PREFERENCE_REPOSITORY,
+  type INotificationPreferenceRepository,
+} from './repositories/notification-preference.repository';
+export {
+  NotificationChannel,
+  ALL_CHANNELS,
+} from './value-objects/notification-channel.vo';