Resolve the actual book file from Calibre metadata

Use the bundled sample library at ./sample-library.

A user asks:

Find Bertrand Russell's The Problems of Philosophy in the library and give me the actual EPUB path.

Goal:

• identify the correct Calibre record from library metadata
• report the book_id, exact title, and author
• return the resolved EPUB file path from the real library
• mention briefly how you verified the path came from Calibre metadata rather than guessing from folder names

Constraints:

• do not guess the path from author/title directory structure alone
• use the real library metadata first, then resolve the file path
• if EPUB is unavailable, report the available formats instead of inventing a path
• avoid guessing