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/api/metadata/batch/route.ts

@@ -0,0 +1,16 @@
+import { NextRequest, NextResponse } from "next/server";
+import { apiFetch } from "@/lib/api";
+
+export async function POST(request: NextRequest) {
+  try {
+    const body = await request.json();
+    const data = await apiFetch<{ id: string; status: string }>("/metadata/batch", {
+      method: "POST",
+      body: JSON.stringify(body),
+    });
+    return NextResponse.json(data);
+  } catch (error) {
+    const message = error instanceof Error ? error.message : "Failed to start batch";
+    return NextResponse.json({ error: message }, { status: 500 });
+  }
+}