feat: add ScanRecord model with toJson

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/models/scan_record.dart

@@ -0,0 +1,21 @@
+enum SendStatus { pending, success, failed }
+
+class ScanRecord {
+  final String barcode;
+  final String codeType;
+  final DateTime timestamp;
+  SendStatus status;
+
+  ScanRecord({
+    required this.barcode,
+    required this.codeType,
+    required this.timestamp,
+    this.status = SendStatus.pending,
+  });
+
+  Map<String, dynamic> toJson() => {
+        'barcode': barcode,
+        'code_type': codeType,
+        'timestamp': timestamp.toUtc().toIso8601String(),
+      };
+}