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/handler/payment_method_handler.go

@@ -113,6 +113,16 @@ func (h *PaymentMethodHandler) ListPaymentMethods(c *gin.Context) {
 
 	req.OrganizationID = &contextInfo.OrganizationID
 
+	// At the cashier, EnakPoint is listed only where the outlet accepts it (F9).
+	if outletStr := c.Query("outlet_id"); outletStr != "" {
+		if outletID, err := uuid.Parse(outletStr); err == nil {
+			req.OutletID = &outletID
+		}
+	} else if contextInfo.OutletID != uuid.Nil {
+		outletID := contextInfo.OutletID
+		req.OutletID = &outletID
+	}
+
 	if isActiveStr := c.Query("is_active"); isActiveStr != "" {
 		if isActive, err := strconv.ParseBool(isActiveStr); err == nil {
 			req.IsActive = &isActive