implemented full interactive poll support in Talk, including creation, voting, and closing functionality

lib/api/marianumcloud/talk/close_poll/close_poll.dart

@@ -0,0 +1,28 @@
+import 'dart:convert';
+
+import 'package:http/http.dart' as http;
+
+import '../../../api_params.dart';
+import '../get_poll/get_poll_state_response.dart';
+import '../talk_api.dart';
+
+/// Schließt eine Umfrage endgültig — nur Ersteller oder Moderatoren.
+class ClosePoll extends TalkApi<GetPollStateResponse> {
+  ClosePoll({required String token, required int pollId})
+    : super('v1/poll/$token/$pollId', null);
+
+  @override
+  GetPollStateResponse assemble(String raw) {
+    final decoded = jsonDecode(raw) as Map<String, dynamic>;
+    return GetPollStateResponse.fromJson(
+      decoded['ocs'] as Map<String, dynamic>,
+    );
+  }
+
+  @override
+  Future<http.Response> request(
+    Uri uri,
+    ApiParams? body,
+    Map<String, String>? headers,
+  ) => http.delete(uri, headers: headers);
+}