The new "Book Downloads" group in Settings holds a Calibre template for the file name of a
direct download. Without a template, the name stays the title. The name is also the title if
the template fails or gives no name for a book.
Plain HTML, CSS and JavaScript modules, with no build step. Hash routes
and relative URLs make it work under any path. The job list is polled:
every 2 seconds while a job runs, and less often otherwise.
tim