markdown support for talk messages

lib/api/marianumcloud/talk/chat/get_chat_response.dart

@@ -42,6 +42,11 @@ class GetChatResponseObject {
   Map<String, RichObjectString>? messageParameters;
   GetChatResponseObject? parent;
 
+  /// Whether the server flagged this message to be rendered as Markdown
+  /// (capability `markdown-messages`). Absent on older servers/messages, in
+  /// which case it stays `false` and the body renders as plain text.
+  bool markdown;
+
   GetChatResponseObject(
     this.id,
     this.token,
@@ -57,8 +62,9 @@ class GetChatResponseObject {
     this.messageParameters,
     this.reactions,
     this.reactionsSelf,
-    this.parent,
-  );
+    this.parent, [
+    this.markdown = false,
+  ]);
 
   factory GetChatResponseObject.fromJson(Map<String, dynamic> json) =>
       _$GetChatResponseObjectFromJson(json);