add traction import export

lib/services/api_service.dart

@@ -105,6 +105,34 @@ class ApiService {
     return _processResponse(response);
   }
 
+  Future<dynamic> postMultipartFile(
+    String endpoint, {
+    required List<int> bytes,
+    required String filename,
+    String fieldName = 'file',
+    Map<String, String>? fields,
+    Map<String, String>? headers,
+  }) async {
+    final request = http.MultipartRequest(
+      'POST',
+      Uri.parse('$baseUrl$endpoint'),
+    );
+    request.headers.addAll(_buildHeaders(headers));
+    if (fields != null && fields.isNotEmpty) {
+      request.fields.addAll(fields);
+    }
+    request.files.add(
+      http.MultipartFile.fromBytes(
+        fieldName,
+        bytes,
+        filename: filename,
+      ),
+    );
+    final streamed = await _client.send(request).timeout(timeout);
+    final response = await http.Response.fromStream(streamed);
+    return _processResponse(response);
+  }
+
   Future<dynamic> postForm(String endpoint, Map<String, String> data) async {
     final response = await _client
         .post(