Add room creation options endpoint and integrate with chat UI: Implement getRoomCreateOptions in ChatController and ChatService, add corresponding API route, and enhance MultiChatDialog for room creation with localized labels and validation. Update i18n files for new room creation features.

frontend/src/api/chatApi.js

@@ -4,3 +4,8 @@ export const fetchPublicRooms = async () => {
   const response = await apiClient.get("/api/chat/rooms");
   return response.data; // expecting array of { id, title, ... }
 };
+
+export const fetchRoomCreateOptions = async () => {
+  const response = await apiClient.get("/api/chat/room-create-options");
+  return response.data;
+};