feat: message format, pretty markdown

backend/src/app_mixins/chat.py

@@ -13,6 +13,7 @@ def message_json(msg):
         "sender": msg.sender,
         "kind": msg.kind,
         "subkind": msg.subkind,
+        "format": msg.format,
         "content": msg.content,
         "threadId": msg.thread_id,
     }

backend/src/server/websocket.py

@@ -276,7 +276,7 @@ def register(server, app, auth_manager):
                 elif action == "update-chat-message":
                     message = await app.update_chat_message(
                         message_id=body['messageId'],
-                        content=body['content'],
+                        content=body.get('content'),
                         kind=body.get('kind'),
                         subkind=body.get('subkind'),
                         format=body.get('format'),