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/globals.css

@@ -706,3 +706,26 @@ button:hover {
 .dark .series-cover {
   background: linear-gradient(135deg, hsl(221 24% 20%), hsl(221 24% 15%));
 }
+
+/* Status badges */
+.status-ok {
+  color: hsl(142 60% 45%);
+  font-weight: 700;
+}
+
+.status-error {
+  color: hsl(2 72% 48%);
+  font-weight: 700;
+}
+
+.status-pending {
+  color: hsl(45 93% 47%);
+  font-weight: 700;
+}
+
+.file-path {
+  font-size: 0.8rem;
+  word-break: break-all;
+  max-width: 400px;
+  display: inline-block;
+}