Extends the GraphQL API so the frontend can replace Open Library:

• searchBooks now returns { books, totalCount } instead of a plain list, so the frontend can show pagination.
• searchBooks orders by id, so limit/offset pagination is stable (no repeated or skipped books between pages).
• New book(id) query for the details page. Returns null if the book doesn't exist.

searchBooks now uses Drizzle's SQL builder instead of the query API, so the same filter can be used for both fetching a page and counting all matches with db.$count.

Tested in Apollo Sandbox:

• searchBooks(title: "harry") gives totalCount 39, matching a direct SQL count.
• Page 1 (offset 0) and page 2 (offset 5) with limit 5 have no books in common, and ids are ascending.
• book(id: 1) returns "The Hunger Games", book(id: 999999) returns null.

I'm new to Drizzle and GraphQL, so I used AI (Claude) for explanations and guidance while writing and testing the code, and to review it before committing.

Closes #30