fix(ui): Harmonize spacing in library sub-pages

- Removed space-y-6 container wrapper
- Added explicit mb-6 margins on breadcrumb, h1, Card, and h2 elements
- Consistent spacing approach across all library pages

apps/backoffice/app/libraries/[id]/series/page.tsx

@@ -0,0 +1,87 @@
+import { fetchLibraries, fetchSeries, getBookCoverUrl, LibraryDto, SeriesDto } from "../../../../lib/api";
+import Image from "next/image";
+import Link from "next/link";
+import { notFound } from "next/navigation";
+import { Card, Badge } from "../../../components/ui";
+
+export const dynamic = "force-dynamic";
+
+export default async function LibrarySeriesPage({
+  params
+}: {
+  params: Promise<{ id: string }>;
+}) {
+  const { id } = await params;
+  
+  const [library, series] = await Promise.all([
+    fetchLibraries().then(libs => libs.find(l => l.id === id)),
+    fetchSeries(id).catch(() => [] as SeriesDto[])
+  ]);
+
+  if (!library) {
+    notFound();
+  }
+
+  return (
+    <>
+      <div className="mb-6">
+        <Link href="/libraries" className="text-sm text-muted hover:text-primary transition-colors">← Back to libraries</Link>
+      </div>
+
+      <h1 className="text-3xl font-bold text-foreground flex items-center gap-3 mb-6">
+        <svg className="w-8 h-8 text-primary" fill="none" stroke="currentColor" viewBox="0 0 24 24"><path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M19 11H5m14 0a2 2 0 012 2v6a2 2 0 01-2 2H5a2 2 0 01-2-2v-6a2 2 0 012-2m14 0V9a2 2 0 00-2-2M5 11V9a2 2 0 012-2m0 0V5a2 2 0 012-2h6a2 2 0 012 2v2M7 7h10" /></svg>
+        {library.name}
+      </h1>
+      
+      <Card className="mb-6">
+        <div className="flex flex-wrap items-center gap-3 text-sm">
+          <code className="text-xs font-mono text-muted bg-muted/10 px-2 py-1 rounded">{library.root_path}</code>
+          <span className="text-muted">|</span>
+          <span className="text-foreground">{library.book_count} book{library.book_count !== 1 ? 's' : ''}</span>
+          <span className="text-muted">|</span>
+          <Badge variant={library.enabled ? "success" : "muted"}>
+            {library.enabled ? "Enabled" : "Disabled"}
+          </Badge>
+        </div>
+      </Card>
+
+      <h2 className="text-xl font-semibold text-foreground mb-6">Series ({series.length})</h2>
+
+      {series.length > 0 ? (
+        <div className="grid grid-cols-2 sm:grid-cols-3 md:grid-cols-4 lg:grid-cols-5 gap-6">
+          {series.map((s) => (
+            <Link 
+              key={s.name} 
+              href={`/libraries/${id}/books?series=${encodeURIComponent(s.name)}`}
+              className="group"
+            >
+              <div className="bg-card rounded-xl shadow-soft border border-line overflow-hidden hover:shadow-card transition-shadow">
+                <div className="aspect-[2/3] relative bg-muted/10">
+                  <Image
+                    src={getBookCoverUrl(s.first_book_id)}
+                    alt={`Cover of ${s.name}`}
+                    fill
+                    className="object-cover"
+                    unoptimized
+                  />
+                </div>
+                <div className="p-3">
+                  <h3 className="font-medium text-foreground truncate text-sm" title={s.name}>
+                    {s.name === "unclassified" ? "Unclassified" : s.name}
+                  </h3>
+                  <p className="text-xs text-muted mt-1">
+                    {s.book_count} book{s.book_count !== 1 ? 's' : ''}
+                  </p>
+                </div>
+              </div>
+            </Link>
+          ))}
+        </div>
+      ) : (
+        <div className="text-center py-12 text-muted">
+          <p>No series found in this library</p>
+        </div>
+      )}
+    </>
+  );
+}