feat: enhance recipe ingredient model; add raw fields and optional properties for better ingredient handling

flutter/lib/features/recipes/domain/inventory_preview.dart

@@ -2,7 +2,7 @@ enum IngredientStatus { enough, missing, unitMismatch }
 
 class IngredientPreview {
   final int ingredientId;
-  final int productId;
+  final int? productId;
   final String productName;
   final double requiredQuantity;
   final String requiredUnit;
@@ -14,7 +14,7 @@ class IngredientPreview {
 
   const IngredientPreview({
     required this.ingredientId,
-    required this.productId,
+    this.productId,
     required this.productName,
     required this.requiredQuantity,
     required this.requiredUnit,
@@ -34,8 +34,8 @@ class IngredientPreview {
     };
     return IngredientPreview(
       ingredientId: json['ingredientId'] as int,
-      productId: json['productId'] as int,
-      productName: json['productName'] as String,
+      productId: (json['productId'] as num?)?.toInt(),
+      productName: (json['productName'] as String?) ?? (json['rawName'] as String? ?? ''),
       requiredQuantity: (json['requiredQuantity'] as num).toDouble(),
       requiredUnit: json['requiredUnit'] as String? ?? '',
       note: json['note'] as String?,