Expose per-product forecast errors

docs/modules/erp/lager/processes/main/erp.lager.stock_lot_forecast_refresh.md

@@ -82,7 +82,8 @@ Nicht erforderlich. Die Produktmenge ist klein; die Verarbeitung erfolgt determi
   "total_products": 0,
   "processed_products": 0,
   "failed_products": 0,
-  "failed_product_ids": []
+  "failed_product_ids": [],
+  "errors": [{"product_id": 0, "message": "..."}]
 }
 ```
 

modules/erp/lager/forecast.php

@@ -187,7 +187,7 @@ function run_lager_stock_lot_forecast(PDO $pdo): array
     $asOfDate = new DateTimeImmutable('today', new DateTimeZone('Europe/Zurich'));
     $result = [
         'status' => 'done', 'total_products' => 0, 'processed_products' => 0,
-        'failed_products' => 0, 'failed_product_ids' => [],
+        'failed_products' => 0, 'failed_product_ids' => [], 'errors' => [],
     ];
 
     try {
@@ -208,6 +208,7 @@ function run_lager_stock_lot_forecast(PDO $pdo): array
             } catch (Throwable $error) {
                 $result['failed_products']++;
                 $result['failed_product_ids'][] = $productId;
+                $result['errors'][] = ['product_id' => $productId, 'message' => $error->getMessage()];
             }
         }
         if ($result['failed_products'] > 0) {