feat(backoffice): add page preview carousel on book detail page

Shows 5 pages at a time in a full-width grid with prev/next navigation.
Pages are fetched via the existing proxy route with webp format.

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

apps/backoffice/app/books/[id]/page.tsx

@@ -1,4 +1,5 @@
 import { fetchLibraries, getBookCoverUrl, BookDto, apiFetch } from "../../../lib/api";
+import { BookPreview } from "../../components/BookPreview";
 import Image from "next/image";
 import Link from "next/link";
 import { notFound } from "next/navigation";
@@ -157,6 +158,12 @@ export default async function BookDetailPage({
           </div>
         </div>
       </div>
+
+      {book.page_count && book.page_count > 0 && (
+        <div className="mt-8">
+          <BookPreview bookId={book.id} pageCount={book.page_count} />
+        </div>
+      )}
     </>
   );
 }

apps/backoffice/app/components/BookPreview.tsx

@@ -0,0 +1,60 @@
+"use client";
+
+import { useState } from "react";
+import Image from "next/image";
+
+const PAGE_SIZE = 5;
+
+export function BookPreview({ bookId, pageCount }: { bookId: string; pageCount: number }) {
+  const [offset, setOffset] = useState(0);
+
+  const pages = Array.from({ length: PAGE_SIZE }, (_, i) => offset + i + 1).filter(
+    (p) => p <= pageCount
+  );
+
+  return (
+    <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
+          <span className="ml-2 text-sm font-normal text-muted-foreground">
+            pages {offset + 1}–{Math.min(offset + PAGE_SIZE, pageCount)} / {pageCount}
+          </span>
+        </h2>
+        <div className="flex gap-2">
+          <button
+            onClick={() => setOffset((o) => Math.max(0, o - PAGE_SIZE))}
+            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
+          </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 →
+          </button>
+        </div>
+      </div>
+
+      <div className="grid grid-cols-5 gap-3">
+        {pages.map((pageNum) => (
+          <div key={pageNum} className="flex flex-col items-center gap-1.5">
+            <div className="relative w-full aspect-[2/3] bg-muted rounded-lg overflow-hidden border border-border">
+              <Image
+                src={`/api/books/${bookId}/pages/${pageNum}?format=webp&width=600&quality=80`}
+                alt={`Page ${pageNum}`}
+                fill
+                className="object-contain"
+                unoptimized
+              />
+            </div>
+            <span className="text-xs text-muted-foreground">{pageNum}</span>
+          </div>
+        ))}
+      </div>
+    </div>
+  );
+}