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/infrastructure/services/fcm.service.ts

@@ -0,0 +1,74 @@
+import { Injectable, type OnModuleInit } from '@nestjs/common';
+import { LoggerService } from '@modules/shared/infrastructure/logger.service';
+import * as admin from 'firebase-admin';
+
+export interface SendPushDto {
+  token: string;
+  title: string;
+  body: string;
+  data?: Record<string, string>;
+}
+
+@Injectable()
+export class FcmService implements OnModuleInit {
+  private initialized = false;
+
+  constructor(private readonly logger: LoggerService) {}
+
+  onModuleInit(): void {
+    const serviceAccountJson = process.env['FIREBASE_SERVICE_ACCOUNT'];
+    if (!serviceAccountJson) {
+      this.logger.warn(
+        'FIREBASE_SERVICE_ACCOUNT not set — push notifications disabled',
+        'FcmService',
+      );
+      return;
+    }
+
+    try {
+      const serviceAccount = JSON.parse(serviceAccountJson) as admin.ServiceAccount;
+      if (!admin.apps.length) {
+        admin.initializeApp({ credential: admin.credential.cert(serviceAccount) });
+      }
+      this.initialized = true;
+      this.logger.log('Firebase Admin initialized for push notifications', 'FcmService');
+    } catch (error) {
+      this.logger.error(
+        `Failed to initialize Firebase: ${error instanceof Error ? error.message : String(error)}`,
+        'FcmService',
+      );
+    }
+  }
+
+  get isAvailable(): boolean {
+    return this.initialized;
+  }
+
+  async send(dto: SendPushDto): Promise<string> {
+    if (!this.initialized) {
+      throw new Error('FCM not initialized — FIREBASE_SERVICE_ACCOUNT not configured');
+    }
+
+    try {
+      const messageId = await admin.messaging().send({
+        token: dto.token,
+        notification: {
+          title: dto.title,
+          body: dto.body,
+        },
+        data: dto.data,
+        android: { priority: 'high' },
+        apns: { payload: { aps: { sound: 'default' } } },
+      });
+
+      this.logger.log(`Push sent to token ${dto.token.slice(0, 10)}...: ${messageId}`, 'FcmService');
+      return messageId;
+    } catch (error) {
+      this.logger.error(
+        `Failed to send push: ${error instanceof Error ? error.message : String(error)}`,
+        'FcmService',
+      );
+      throw error;
+    }
+  }
+}