Parser:
- Change volume type from Option<String> to Option<i32>
- Parse volume as integer to remove leading zeros
- Keep original title with volume info
Indexer:
- Update SQL queries to insert volume as integer
- Add volume column to INSERT and UPDATE statements
API:
- Change BookItem.volume and BookDetails.volume to Option<i32>
- Add natural sorting for books
Backoffice:
- Update volume type to number
- Update book detail page
- Add CSS styles
