Bulk-deleting source epub/audio and cache files after processing instead of one book at a time

I want to convert every book I add and then drop the original epub and audio files, keeping only the synced EPUB 3. The UI only exposes a per-book delete, which is not workable with a library of a hundred-plus processed books.

Resolution: There is no per-book-only limitation any more: a setting was added to clear the intermediate/cached files automatically after processing completes, plus a bulk action to delete them for many books at once. Enable the automatic cleanup in settings if you never want the transcoded audio kept, and use the bulk action for the backlog you already processed. This is server/container UI functionality — if you drive alignment through the CLI instead, you are managing the intermediates yourself and neither the setting nor the bulk action applies. Deleting these files is safe for playback because the finished readaloud EPUB embeds its own audio.