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/repository/payment_method_repository.go

@@ -75,6 +75,8 @@ func (r *PaymentMethodRepositoryImpl) List(ctx context.Context, filters map[stri
 		case "search":
 			searchValue := "%" + value.(string) + "%"
 			query = query.Where("name ILIKE ? OR processor ILIKE ?", searchValue, searchValue)
+		case "exclude_type":
+			query = query.Where("type <> ?", value)
 		default:
 			query = query.Where(key+" = ?", value)
 		}