feat: enhance receipt import functionality with category selection and PDF opening support

flutter/lib/features/import/data/receipt_import_session.dart

@@ -6,11 +6,16 @@ import '../domain/parsed_receipt_item.dart';
 
 enum ImportDestination { inventory, pantry }
 
+enum CategorySelectionSource { ai, manual }
+
 // ── Per-rad redigeringstillstånd ──────────────────────────────────────────────
 
 class ItemEdit {
   final int? productId;
   final String? productName;
+  final int? categoryId;
+  final String? categoryPath;
+  final CategorySelectionSource? categorySource;
   final double? quantity;
   final String? unit;
   final ImportDestination destination;
@@ -18,6 +23,9 @@ class ItemEdit {
   const ItemEdit({
     this.productId,
     this.productName,
+    this.categoryId,
+    this.categoryPath,
+    this.categorySource,
     this.quantity,
     this.unit,
     this.destination = ImportDestination.inventory,