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/lib/api.ts

@@ -37,9 +37,12 @@ export type BookDto = {
   title: string;
   author: string | null;
   series: string | null;
-  volume: string | null;
+  volume: number | null;
   language: string | null;
   page_count: number | null;
+  file_path: string | null;
+  file_format: string | null;
+  file_parse_status: string | null;
   updated_at: string;
 };
 
@@ -54,7 +57,7 @@ export type SearchHitDto = {
   title: string;
   author: string | null;
   series: string | null;
-  volume: string | null;
+  volume: number | null;
   kind: string;
   language: string | null;
 };