feat: move native communication to FFI (#1457)

ui/flutter/test/core/common/task_event_test.dart

@@ -0,0 +1,24 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:gopeed/core/common/task_event.dart';
+
+void main() {
+  test('task event mask combines subscribed event types', () {
+    expect({TaskEventType.done}.mask, 1);
+    expect({TaskEventType.error}.mask, 2);
+    expect({TaskEventType.done, TaskEventType.error}.mask, 3);
+  });
+
+  test('task event decodes terminal payload', () {
+    final event = TaskEvent.fromJson({
+      'type': 'task.error',
+      'taskId': 'task-1',
+      'name': 'archive.zip',
+      'error': 'network error',
+    });
+
+    expect(event.type, TaskEventType.error);
+    expect(event.taskId, 'task-1');
+    expect(event.name, 'archive.zip');
+    expect(event.error, 'network error');
+  });
+}