feat: add nullable outlet_id to product

internal/handler/product_handler.go

@@ -172,6 +172,12 @@ func (h *ProductHandler) ListProducts(c *gin.Context) {
 		}
 	}
 
+	if outletIDStr := c.Query("outlet_id"); outletIDStr != "" {
+		if outletID, err := uuid.Parse(outletIDStr); err == nil {
+			req.OutletID = &outletID
+		}
+	}
+
 	if categoryIDStr := c.Query("category_id"); categoryIDStr != "" {
 		if categoryID, err := uuid.Parse(categoryIDStr); err == nil {
 			req.CategoryID = &categoryID