⚡ Bolt: Optimize library list query performance

[jspann21]

💡 What: Added a CTE to limit the intermediate result set in find_book_by_title_author_conn.
🎯 Why: In large libraries, failing to limit the rows before a GROUP BY and LEFT JOIN on book_files creates a full table scan that severely impacts performance during background tasks and auto-matching.
📊 Impact: Prevents N+1 bottlenecks by bounding the inner query to 200 records prior to aggregation, bounding execution time to O(1) relative to library scale instead of O(N).
🔬 Measurement: Verify by executing large library test suites (e.g. cargo test --manifest-path src-tauri/Cargo.toml) and observing stable execution times regardless of database scale.

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PR created automatically by Jules for task 9877300629532606772 started by @jspann21

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