This commit adds the tree_structure.json file to the assets directory, which contains the initial skill tree structure. This JSON file will serve as the data source for rendering the skill tree nodes and edges in the application.
Added the downloadArtifact method to the ChatService class, enabling the download of artifacts in the Flutter web application. The function uses the dart:html package to trigger a browser-based file download, allowing users to save artifacts locally. This implementation complements the existing REST API and enhances the user experience.
