feat: Implement report download as markdown#10

This commit introduces a "Download Report" button on the report details page. When clicked, this button triggers the download of the report content as a markdown file named "report.md". The changes include: - Added a "Download Report" button to the `TopBar` in `src/index.tsx` for the report details view. - Implemented a JavaScript function `downloadReport(filename, content)` in `src/static/core.js` to handle the file creation and download trigger. - Connected the button's `onClick` event to this JavaScript function, passing the report's raw markdown content. - Verified that `core.js` is included in the main layout.