Refactor the PDF handling feature to support multiple files per artifact.

Replace the current single-file lookup (based on the page directory) with a directory-based retrieval approach:

- Locate the 'PDF' directory associated with the current artifact.
- Enumerate all files with a .pdf extension in that directory.
- Populate a UI menu component with the list of PDFs.
- Bind the PDF button to toggle/display this menu instead of initiating a direct download.
- Each menu item should trigger 'open in new tab' behavior for its respective PDF.

Ensure the solution dynamically reflects changes in the folder (no hardcoding of filenames).
