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

lib/api/marianumcloud/talk/vote_poll/vote_poll.dart

@@ -0,0 +1,41 @@
+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';
+import 'vote_poll_params.dart';
+
+class VotePoll extends TalkApi<GetPollStateResponse> {
+  // Body als echtes JSON (nicht form-encoded wie die anderen Endpunkte): nur
+  // so kommt das int-Array an; sonst liest der Server optionIds als [] und
+  // löscht die eigene Stimme (Ursache des Readonly-Fallbacks, Issue #42).
+  VotePoll({
+    required String token,
+    required int pollId,
+    required VotePollParams params,
+  }) : super(
+         'v1/poll/$token/$pollId',
+         params,
+         headers: {'Content-Type': 'application/json'},
+       );
+
+  @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,
+  ) {
+    if (body is! VotePollParams) return null;
+    return http.post(uri, headers: headers, body: jsonEncode(body.toJson()));
+  }
+}