feat: add metadata refresh job to re-download metadata for linked series

Adds a new job type that refreshes metadata from external providers for
all series already linked via approved external_metadata_links. Tracks
and displays per-field diffs (series and book level), respects locked
fields, and provides a detailed change report in the job detail page.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/backoffice/app/components/ui/Badge.tsx

@@ -114,6 +114,7 @@ export function JobTypeBadge({ type, className = "" }: JobTypeBadgeProps) {
     thumbnail_regenerate: t("jobType.thumbnail_regenerate"),
     cbr_to_cbz: t("jobType.cbr_to_cbz"),
     metadata_batch: t("jobType.metadata_batch"),
+    metadata_refresh: t("jobType.metadata_refresh"),
   };
   const label = jobTypeLabels[key] ?? type;
   return <Badge variant={variant} className={className}>{label}</Badge>;