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>

prisma/schema.prisma

@@ -476,6 +476,56 @@ model MarketIndex {
   @@index([city, period])
 }
 
+// =============================================================================
+// NOTIFICATIONS
+// =============================================================================
+
+enum NotificationChannel {
+  EMAIL
+  SMS
+  PUSH
+  ZALO_OA
+}
+
+enum NotificationStatus {
+  PENDING
+  SENT
+  FAILED
+  DELIVERED
+}
+
+model NotificationLog {
+  id          String             @id @default(cuid())
+  userId      String
+  channel     NotificationChannel
+  templateKey String
+  subject     String?
+  body        String             @db.Text
+  metadata    Json?
+  status      NotificationStatus @default(PENDING)
+  errorDetail String?
+  sentAt      DateTime?
+  createdAt   DateTime           @default(now())
+
+  @@index([userId])
+  @@index([channel, status])
+  @@index([templateKey])
+  @@index([createdAt])
+}
+
+model NotificationPreference {
+  id        String              @id @default(cuid())
+  userId    String
+  channel   NotificationChannel
+  eventType String
+  enabled   Boolean             @default(true)
+  createdAt DateTime            @default(now())
+  updatedAt DateTime            @updatedAt
+
+  @@unique([userId, channel, eventType])
+  @@index([userId])
+}
+
 // =============================================================================
 // REVIEWS
 // =============================================================================