feat: add receipt import session management with file handling and item editing support

flutter/lib/core/ui/category_then_product_picker.dart

@@ -47,6 +47,7 @@ class CategoryThenProductPicker {
     required List<ProductOption> products,
     int? currentProductId,
     int? preselectedCategoryId,
+    String? initialQuery,
     Future<ProductOption?> Function(String name, int categoryId)? onCreate,
   }) async {
     AdminCategoryNode? selectedCategory;
@@ -94,6 +95,7 @@ class CategoryThenProductPicker {
       value: currentProductId,
       label: 'Produkt i "${selectedCategory!.name}"',
       categoryFilter: null, // redan förfiltrerat
+      initialQuery: initialQuery,
       onCreate: onCreateBound,
     );
   }