feat(customer): list the customer's outlets

Adds GET /customer/outlets for the customer app: the active outlets of the
customer's organization, where their EnakPoint and EnakCoin can be used,
sorted by name. Each carries its name and address, and from the outlet's
loyalty settings whether the cashier accepts EnakPoint and whether orders
there earn EnakPoint or EnakCoin. Nothing internal (printer settings, tax
rate) is exposed.

The outlets list under /outlets needs a staff token, so the app had no way
to show where the wallet works.

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

internal/repository/customer_outlet_repository.go

@@ -0,0 +1,60 @@
+package repository
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/google/uuid"
+	"gorm.io/gorm"
+)
+
+// CustomerOutlet is what the customer app may see of an outlet.
+type CustomerOutlet struct {
+	ID      uuid.UUID
+	Name    string
+	Address *string
+}
+
+// CustomerOutletRepository reads the outlets a customer can visit: the active outlets
+// of their organization.
+type CustomerOutletRepository interface {
+	// CustomerOrganizationID returns ErrWalletNotFound when the customer does not exist.
+	CustomerOrganizationID(ctx context.Context, customerID uuid.UUID) (uuid.UUID, error)
+	// ListActiveOutlets returns the organization's active outlets, by name.
+	ListActiveOutlets(ctx context.Context, organizationID uuid.UUID) ([]CustomerOutlet, error)
+}
+
+type customerOutletRepository struct {
+	db *gorm.DB
+}
+
+func NewCustomerOutletRepository(db *gorm.DB) CustomerOutletRepository {
+	return &customerOutletRepository{db: db}
+}
+
+func (r *customerOutletRepository) CustomerOrganizationID(ctx context.Context, customerID uuid.UUID) (uuid.UUID, error) {
+	var row struct{ OrganizationID uuid.UUID }
+	err := DBFromContext(ctx, r.db).WithContext(ctx).
+		Table("customers").Select("organization_id").Where("id = ?", customerID).Take(&row).Error
+	if err != nil {
+		if errors.Is(err, gorm.ErrRecordNotFound) {
+			return uuid.Nil, ErrWalletNotFound
+		}
+		return uuid.Nil, fmt.Errorf("failed to get customer organization: %w", err)
+	}
+	return row.OrganizationID, nil
+}
+
+func (r *customerOutletRepository) ListActiveOutlets(ctx context.Context, organizationID uuid.UUID) ([]CustomerOutlet, error) {
+	var outlets []CustomerOutlet
+	err := DBFromContext(ctx, r.db).WithContext(ctx).
+		Table("outlets").Select("id, name, address").
+		Where("organization_id = ? AND is_active = ?", organizationID, true).
+		Order("name, id").
+		Scan(&outlets).Error
+	if err != nil {
+		return nil, fmt.Errorf("failed to list outlets: %w", err)
+	}
+	return outlets, nil
+}