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/BookPreview.tsx

@@ -16,7 +16,7 @@ export function BookPreview({ bookId, pageCount }: { bookId: string; pageCount:
     <div className="bg-card rounded-xl border border-border p-6">
       <div className="flex items-center justify-between mb-4">
         <h2 className="text-lg font-semibold text-foreground">
-          Preview
+          Aperçu
           <span className="ml-2 text-sm font-normal text-muted-foreground">
             pages {offset + 1}–{Math.min(offset + PAGE_SIZE, pageCount)} / {pageCount}
           </span>
@@ -27,14 +27,14 @@ export function BookPreview({ bookId, pageCount }: { bookId: string; pageCount:
             disabled={offset === 0}
             className="px-3 py-1.5 text-sm rounded-lg border border-border bg-muted/50 text-foreground hover:bg-muted disabled:opacity-40 disabled:cursor-not-allowed transition-colors"
           >
-            ← Prev
+            ← Préc.
           </button>
           <button
             onClick={() => setOffset((o) => Math.min(o + PAGE_SIZE, pageCount - 1))}
             disabled={offset + PAGE_SIZE >= pageCount}
             className="px-3 py-1.5 text-sm rounded-lg border border-border bg-muted/50 text-foreground hover:bg-muted disabled:opacity-40 disabled:cursor-not-allowed transition-colors"
           >
-            Next →
+            Suiv. →
           </button>
         </div>
       </div>