feat: change volume from string to integer type

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

apps/backoffice/app/books/page.tsx

@@ -36,6 +36,9 @@ export default async function BooksPage({
         volume: hit.volume,
         language: hit.language,
         page_count: null,
+        file_path: null,
+        file_format: null,
+        file_parse_status: null,
         updated_at: ""
       }));
       totalHits = searchResponse.estimated_total_hits;