feat(loyalty): EnakPoint payment method

Adds the system payment method for paying with EnakPoint
(docs/prd-point-coin.md F9, §8, §10.5, PC-303).

Migration 000094 allows the point type, keeps one per organization with a
partial unique index, creates it for every existing organization, and adds
a trigger that creates it for new ones, as the walk-in customer is. It adds
payments.points_used and point_value. Their CHECK is written so it can
never be NULL: the PRD form, (both NULL) OR (both > 0), is NULL for
points_used with a NULL point_value, which a CHECK lets through, so a
payment could have lost the value a refund depends on. A test caught it.

The API cannot create, delete or retype the EnakPoint method, nor turn
another method into one; that answers 400. Renaming it is allowed. The
method list takes the outlet from ?outlet_id= or the user's outlet and
leaves EnakPoint out when that outlet does not accept it, filtered in the
query so the count stays right. The organization-wide active list is
unchanged.

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

internal/processor/payment_method_processor.go

@@ -1,7 +1,10 @@
 package processor
 
 import (
+	"apskel-pos-be/internal/constants"
+	"apskel-pos-be/internal/entities"
 	"context"
+	"errors"
 	"fmt"
 
 	"apskel-pos-be/internal/mappers"
@@ -20,17 +23,26 @@ type PaymentMethodProcessor interface {
 	GetActivePaymentMethodsByOrganization(ctx context.Context, organizationID uuid.UUID) ([]models.PaymentMethodResponse, error)
 }
 
+// ErrSystemPaymentMethod means an attempt to create, delete or retype the EnakPoint
+// method, which the system owns (docs/prd-point-coin.md F9).
+var ErrSystemPaymentMethod = errors.New("the EnakPoint payment method is managed by the system: it cannot be created, deleted or change type")
+
 type PaymentMethodProcessorImpl struct {
 	paymentMethodRepo repository.PaymentMethodRepository
+	outletSettings    outletSettingsReader
 }
 
-func NewPaymentMethodProcessorImpl(paymentMethodRepo repository.PaymentMethodRepository) *PaymentMethodProcessorImpl {
+func NewPaymentMethodProcessorImpl(paymentMethodRepo repository.PaymentMethodRepository, outletSettings outletSettingsReader) *PaymentMethodProcessorImpl {
 	return &PaymentMethodProcessorImpl{
 		paymentMethodRepo: paymentMethodRepo,
+		outletSettings:    outletSettings,
 	}
 }
 
 func (p *PaymentMethodProcessorImpl) CreatePaymentMethod(ctx context.Context, req *models.CreatePaymentMethodRequest) (*models.PaymentMethodResponse, error) {
+	if req.Type == constants.PaymentMethodTypePoint {
+		return nil, ErrSystemPaymentMethod
+	}
 	exists, err := p.paymentMethodRepo.ExistsByName(ctx, req.OrganizationID, req.Name, nil)
 	if err != nil {
 		return nil, fmt.Errorf("failed to check payment method name uniqueness: %w", err)
@@ -77,6 +89,17 @@ func (p *PaymentMethodProcessorImpl) ListPaymentMethods(ctx context.Context, req
 	if req.Search != "" {
 		filters["search"] = req.Search
 	}
+	// At the cashier EnakPoint only shows where the outlet accepts it (F9). Filtered in
+	// the query so paging stays right.
+	if req.OutletID != nil && p.outletSettings != nil {
+		settings, err := p.outletSettings.Outlet(ctx, *req.OutletID)
+		if err != nil {
+			return nil, fmt.Errorf("failed to read outlet loyalty settings: %w", err)
+		}
+		if !settings.PointPayment.AcceptPayment {
+			filters["exclude_type"] = string(constants.PaymentMethodTypePoint)
+		}
+	}
 
 	offset := (req.Page - 1) * req.Limit
 
@@ -116,6 +139,15 @@ func (p *PaymentMethodProcessorImpl) UpdatePaymentMethod(ctx context.Context, id
 		return nil, fmt.Errorf("payment method not found: %w", err)
 	}
 
+	// The EnakPoint method keeps its type, and no other method can become one.
+	if req.Type != nil {
+		wasPoint := existingPaymentMethod.Type == entities.PaymentMethodTypePoint
+		isPoint := *req.Type == constants.PaymentMethodTypePoint
+		if wasPoint != isPoint {
+			return nil, ErrSystemPaymentMethod
+		}
+	}
+
 	// Check name uniqueness if name is being updated
 	if req.Name != nil && *req.Name != existingPaymentMethod.Name {
 		exists, err := p.paymentMethodRepo.ExistsByName(ctx, existingPaymentMethod.OrganizationID, *req.Name, &id)
@@ -147,10 +179,13 @@ func (p *PaymentMethodProcessorImpl) UpdatePaymentMethod(ctx context.Context, id
 
 func (p *PaymentMethodProcessorImpl) DeletePaymentMethod(ctx context.Context, id uuid.UUID) error {
 	// Check if payment method exists
-	_, err := p.paymentMethodRepo.GetByID(ctx, id)
+	existing, err := p.paymentMethodRepo.GetByID(ctx, id)
 	if err != nil {
 		return fmt.Errorf("payment method not found: %w", err)
 	}
+	if existing.Type == entities.PaymentMethodTypePoint {
+		return ErrSystemPaymentMethod
+	}
 
 	// TODO: Check if payment method is being used in any payments
 	// For now, allow deletion