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/Icon.tsx

@@ -31,7 +31,9 @@ type IconName =
   | "play"
   | "stop"
   | "spinner"
-  | "warning";
+  | "warning"
+  | "tag"
+  | "document";
 
 type IconSize = "sm" | "md" | "lg" | "xl";
 
@@ -82,6 +84,8 @@ const icons: Record<IconName, string> = {
   stop: "M21 12a9 9 0 11-18 0 9 9 0 0118 0z M9 10a1 1 0 011-1h4a1 1 0 011 1v4a1 1 0 01-1 1h-4a1 1 0 01-1-1v-4z",
   spinner: "M4 4v5h.582m15.582 0A8.001 8.001 0 004.582 9m0 0H9m11 11v-5h-.581m0 0a8.003 8.003 0 01-15.357-2m15.357 2H15",
   warning: "M12 9v2m0 4h.01m-6.938 4h13.856c1.54 0 2.502-1.667 1.732-3L13.732 4c-.77-1.333-2.694-1.333-3.464 0L3.34 16c-.77 1.333.192 3 1.732 3z",
+  tag: "M7 7h.01M7 3h5a1.99 1.99 0 011.414.586l7 7a2 2 0 010 2.828l-7 7a2 2 0 01-2.828 0l-7-7A1.994 1.994 0 013 12V7a4 4 0 014-4z",
+  document: "M9 12h6m-6 4h6m2 5H7a2 2 0 01-2-2V5a2 2 0 012-2h5.586a1 1 0 01.707.293l5.414 5.414a1 1 0 01.293.707V19a2 2 0 01-2 2z",
 };
 
 const colorClasses: Partial<Record<IconName, string>> = {