feat: add batch metadata jobs, series filters, and translate backoffice to French

- Add metadata_batch job type with background processing via tokio::spawn
- Auto-apply metadata only when single result at 100% confidence
- Support primary + fallback provider per library, "none" to opt out
- Add batch report/results API endpoints and job detail UI
- Add series_status and has_missing filters to both series listing pages
- Add GET /series/statuses endpoint for dynamic filter options
- Normalize series_metadata status values (migration 0036)
- Hide ComicVine provider tab when no API key configured
- Translate entire backoffice UI from English to French

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

apps/backoffice/app/components/FolderBrowser.tsx

@@ -173,7 +173,7 @@ export function FolderBrowser({ initialFolders, selectedPath, onSelect }: Folder
       <div className="max-h-80 overflow-y-auto">
         {tree.length === 0 ? (
           <div className="px-3 py-8 text-sm text-muted-foreground text-center">
-            No folders found
+            Aucun dossier trouvé
           </div>
         ) : (
           tree.map(node => renderNode(node))