fix: handle empty results, and download into the library folder

fix: handle empty results, and download into the library folder Two fixes found while testing on a Kindle PW4: - All Lists / Bookmarks / a single list returned nil when the API legitimately had nothing to show, which surfaced as the opaque 'Failed to load view data'. An account with zero lists could not open the All Lists view at all. Empty responses are now a normal empty state with a dimmed placeholder row. - Downloads went to /karakeep/, i.e. inside KOReader's own data directory, where they never appear alongside the user's books. They now go to /Karakeep/ when a home folder is set (/mnt/us/documents/Karakeep on Kindle), so downloaded articles show up in the file manager and in cover-browser home screens. Falls back to the old location when no home folder is configured.