Backend:
- GET /api/files/{md5}/neighbors/ returns previous/next items in the
current ordering (name, size, created_at) for keyboard navigation
Frontend:
- / focuses the library search input
- D downloads the file on the detail page
- [ and ] navigate to the previous/next item; hint shown on the page
- Ctrl/Cmd+K opens a command palette (navigation, toggle filters,
focus search, log in/out); Escape closes it
- Sort order now persists alongside the other library filters so
prev/next stays consistent