Goal
Given a username and book_title, find the best matching book in the user's LiveLib reading list and return a canonical https://www.livelib.ru/book/... URL.
Inputs
username(string)book_title(string)
Output
book_url(string | null)candidates(list)
Notes
- Prefer exact title matches; otherwise choose the closest candidate.
- If no candidate is found, return
book_url = null.
See references in references/.