- Add spine-move-book: move book between shelves by cutting/pasting headline
- Add spine-set-status: change TODO keyword (WANT/READING/READ/none)
- Add action=shelf and action=status cases to httpd/edit POST handler
- Wrap shelf/status selects in forms with onchange auto-submit to /edit
- Wire note composer as POST form to /edit with action=note
- Redirect all edit POSTs back to /book?id=X
- 7 new tests for move-book and set-status (error handling, property preservation)