Implement a rich file preview interface to allow users to view file
contents directly in the browser.
Changes include:
- Exposing raw file size (`SizeBytes`) in the download handler's file view.
- Adding comprehensive CSS styling for the preview layout and cards.
- Integrating Prism.js for syntax highlighting of code files.
- Updating Content Security Policy (CSP) headers to permit inline styles and frame sources required by the preview components.
- Adding unit tests to ensure preview metadata attributes are correctly rendered on the download page.
