feat(loyalty): notify transfer recipients through FCM

The recipient of a transfer now gets a push through FCM instead of a
WhatsApp message (docs/prd-point-coin.md F5).

Customers had nowhere to keep FCM tokens: user_devices only holds staff
devices. Migration 000096 adds customer_devices, and the customer app
registers with PUT /customer/devices { device_id, fcm_token, platform,
app_version } after login and whenever FCM refreshes the token, and
unregisters with DELETE /customer/devices/:device_id on logout. A token
belongs to one customer only: registering it takes it away from whoever
had it on that phone before, so they stop getting this customer's
notifications.

The push goes to every device of the recipient after the commit, titled
"EnakPoint masuk" or "EnakCoin masuk", with type WALLET_TRANSFER_IN, the
TRANSFER_IN transaction id, the group id, the currency and the amount in
its data so the app can open it. A retried transfer sends nothing again. It
stays best effort: no device, FCM not configured or FCM failing is logged
and never undoes the transfer.

The app builds one FCM client and shares it between staff notifications
and customer pushes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/app/app.go

@@ -160,6 +160,7 @@ func (a *App) Initialize(cfg *config.Config) error {
 		services.pointPaymentService,
 		services.customerOrderPaymentService,
 		services.customerWalletService,
+		services.customerDeviceService,
 		a.redisClient,
 	)
 
@@ -396,10 +397,14 @@ type processors struct {
 	walletExchangeProcessor             *processor.WalletExchangeProcessor
 	walletTransferProcessor             *processor.WalletTransferProcessor
 	walletTraceProcessor                *processor.WalletTraceProcessor
+	customerDeviceProcessor             *processor.CustomerDeviceProcessor
 }
 
 func (a *App) initProcessors(cfg *config.Config, repos *repositories) *processors {
 	fileClient := client.NewFileClient(cfg.S3Config)
+	fcmClient := buildFCMClient(cfg)
+	// Devices of the customer app, for pushes through FCM
+	customerDeviceProcessor := processor.NewCustomerDeviceProcessor(repository.NewCustomerDeviceRepository(a.db), fcmClient)
 	fonnteClient := client.NewFonnteClient(cfg.GetFonnte())
 	otpProcessor := processor.NewOtpProcessor(fonnteClient, repos.otpRepo)
 	// Customer PIN (docs/prd-point-coin.md F11)
@@ -417,8 +422,8 @@ func (a *App) initProcessors(cfg *config.Config, repos *repositories) *processor
 	orderProcessor.SetPointPayments(pointPaymentProcessor, paymentCodeProcessor, customerPinProcessor)
 	// Exchange EnakCoin into EnakPoint, approved by the customer's PIN (docs/prd-point-coin.md F4)
 	walletExchangeProcessor := processor.NewWalletExchangeProcessor(repository.NewWalletMoveRepository(a.db), loyaltySettingsProcessor, repos.walletQueryRepo, customerPinProcessor, processor.NewWalletProcessor(repos.walletRepo), repos.txManager)
-	// Send EnakPoint or EnakCoin to another customer; the recipient is told by WhatsApp (docs/prd-point-coin.md F5)
-	walletTransferProcessor := processor.NewWalletTransferProcessor(repository.NewWalletMoveRepository(a.db), loyaltySettingsProcessor, repos.walletQueryRepo, customerPinProcessor, processor.NewWalletProcessor(repos.walletRepo), repos.txManager, otpProcessor)
+	// Send EnakPoint or EnakCoin to another customer; the recipient gets a push through FCM (docs/prd-point-coin.md F5)
+	walletTransferProcessor := processor.NewWalletTransferProcessor(repository.NewWalletMoveRepository(a.db), loyaltySettingsProcessor, repos.walletQueryRepo, customerPinProcessor, processor.NewWalletProcessor(repos.walletRepo), repos.txManager, customerDeviceProcessor)
 
 	return &processors{
 		userProcessor:                       processor.NewUserProcessor(repos.userRepo, repos.organizationRepo, repos.outletRepo),
@@ -461,7 +466,7 @@ func (a *App) initProcessors(cfg *config.Config, repos *repositories) *processor
 		fileClient:                          fileClient,
 		inventoryMovementService:            inventoryMovementService,
 		userDeviceProcessor:                 processor.NewUserDeviceProcessorImpl(repos.userDeviceRepo),
-		notificationProcessor:               buildNotificationProcessor(cfg, repos),
+		notificationProcessor:               buildNotificationProcessor(repos, fcmClient),
 		productOutletPriceProcessor:         processor.NewProductOutletPriceProcessorImpl(repos.productOutletPriceRepo, repos.productRepo, repos.outletRepo),
 		expenseProcessor:                    processor.NewExpenseProcessorImpl(repos.expenseRepo, repos.purchaseCategoryRepo, repos.cashAdvanceRepo),
 		cashAdvanceProcessor:                processor.NewCashAdvanceProcessorImpl(repos.cashAdvanceRepo, repos.categoryRepo),
@@ -474,6 +479,7 @@ func (a *App) initProcessors(cfg *config.Config, repos *repositories) *processor
 		walletExchangeProcessor:             walletExchangeProcessor,
 		walletTransferProcessor:             walletTransferProcessor,
 		walletTraceProcessor:                processor.NewWalletTraceProcessor(repository.NewWalletTraceRepository(a.db)),
+		customerDeviceProcessor:             customerDeviceProcessor,
 		walletAdminProcessor:                processor.NewWalletAdminProcessor(repository.NewWalletAdminRepository(a.db), repos.walletQueryRepo, processor.NewWalletProcessor(repos.walletRepo), repos.txManager),
 	}
 }
@@ -523,6 +529,7 @@ type services struct {
 	pointPaymentService               *service.PointPaymentServiceImpl
 	customerOrderPaymentService       *service.CustomerOrderPaymentServiceImpl
 	customerWalletService             *service.CustomerWalletServiceImpl
+	customerDeviceService             *service.CustomerDeviceServiceImpl
 }
 
 func (a *App) initServices(processors *processors, repos *repositories, cfg *config.Config) *services {
@@ -610,6 +617,7 @@ func (a *App) initServices(processors *processors, repos *repositories, cfg *con
 		pointPaymentService:               service.NewPointPaymentService(processors.pointPaymentProcessor),
 		customerOrderPaymentService:       service.NewCustomerOrderPaymentService(processors.orderProcessor),
 		customerWalletService:             service.NewCustomerWalletService(processors.walletExchangeProcessor, processors.walletTransferProcessor),
+		customerDeviceService:             service.NewCustomerDeviceService(processors.customerDeviceProcessor),
 	}
 }
 
@@ -693,19 +701,23 @@ func (a *App) initValidators() *validators {
 	}
 }
 
+// buildFCMClient connects to FCM, or returns nil when it is not configured or fails to
+// start. FCM failing is non-fatal: pushes are skipped and notifications are still
+// persisted.
+func buildFCMClient(cfg *config.Config) client.FCMClient {
+	if cfg.FCM.CredentialsFile == "" {
+		return nil
+	}
+	fcmClient, err := client.NewFCMClient(&cfg.FCM)
+	if err != nil {
+		return nil
+	}
+	return fcmClient
+}
+
 // buildNotificationProcessor creates the notification processor with FCM integration.
 // If FCM is not configured, it returns a processor with a nil FCM client (FCM dispatch will be skipped).
-func buildNotificationProcessor(cfg *config.Config, repos *repositories) *processor.NotificationProcessorImpl {
-	var fcmClient client.FCMClient
-	if cfg.FCM.CredentialsFile != "" {
-		var err error
-		fcmClient, err = client.NewFCMClient(&cfg.FCM)
-		if err != nil {
-			// FCM init failure is non-fatal; notifications will still be persisted.
-			fcmClient = nil
-		}
-	}
-
+func buildNotificationProcessor(repos *repositories, fcmClient client.FCMClient) *processor.NotificationProcessorImpl {
 	return processor.NewNotificationProcessor(
 		repos.notificationRepo,
 		repos.notificationReceiverRepo,