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/app.module.ts

@@ -1,5 +1,6 @@
 import { SharedModule } from '@modules/shared';
 import { AuthModule } from '@modules/auth';
+import { NotificationsModule } from '@modules/notifications';
 import { Module } from '@nestjs/common';
 import { APP_GUARD } from '@nestjs/core';
 import { CqrsModule } from '@nestjs/cqrs';
@@ -12,6 +13,7 @@ import { AppController } from './app.controller';
     CqrsModule.forRoot(),
     SharedModule,
     AuthModule,
+    NotificationsModule,
 
     // ── Rate Limiting ──
     // Default: 60 requests per 60 seconds per IP