feat: implement AI recipe suggestions; add endpoint and UI for generating suggestions based on inventory

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

@@ -10,6 +10,7 @@ class IngredientPreview {
   final double availableQuantity;
   final IngredientStatus status;
   final double missingQuantity;
+  final bool fromPantry;
 
   const IngredientPreview({
     required this.ingredientId,
@@ -21,6 +22,7 @@ class IngredientPreview {
     required this.availableQuantity,
     required this.status,
     required this.missingQuantity,
+    this.fromPantry = false,
   });
 
   factory IngredientPreview.fromJson(Map<String, dynamic> json) {
@@ -40,6 +42,7 @@ class IngredientPreview {
       availableQuantity: (json['availableQuantity'] as num? ?? 0).toDouble(),
       status: status,
       missingQuantity: (json['missingQuantity'] as num? ?? 0).toDouble(),
+      fromPantry: json['fromPantry'] as bool? ?? false,
     );
   }
 }
@@ -50,6 +53,7 @@ class PreviewSummary {
   final int missingCount;
   final int unitMismatchCount;
   final bool canCookExactly;
+  final int pantryCount;
 
   const PreviewSummary({
     required this.totalIngredients,
@@ -57,6 +61,7 @@ class PreviewSummary {
     required this.missingCount,
     required this.unitMismatchCount,
     required this.canCookExactly,
+    this.pantryCount = 0,
   });
 
   factory PreviewSummary.fromJson(Map<String, dynamic> json) {
@@ -66,6 +71,7 @@ class PreviewSummary {
       missingCount: json['missingCount'] as int,
       unitMismatchCount: json['unitMismatchCount'] as int,
       canCookExactly: json['canCookExactly'] as bool? ?? false,
+      pantryCount: json['pantryCount'] as int? ?? 0,
     );
   }
 }