feat: add series support for book organization

API:
- Add /libraries/{id}/series endpoint to list series with book counts
- Add series filter to /books endpoint
- Fix SeriesItem to return first_book_id properly (using CTE with ROW_NUMBER)

Indexer:
- Parse series from parent folder name relative to library root
- Store series in database when indexing books

Backoffice:
- Add Books page with grid view, search, and pagination
- Add Series page showing series with cover images
- Add Library books page filtered by series
- Add book detail page
- Add Series column in libraries list with clickable link
- Create BookCard component for reusable book display
- Add CSS styles for books grid, series grid, and book details
- Add proxy API route for book cover images (fixing CORS issues)

Parser:
- Add series field to ParsedMetadata
- Extract series from file path relative to library root

Books without a parent folder are categorized as 'unclassified' series.

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

@@ -0,0 +1,99 @@
+import { fetchLibraries, getBookCoverUrl, BookDto, apiFetch } from "../../../lib/api";
+import Image from "next/image";
+import Link from "next/link";
+import { notFound } from "next/navigation";
+
+export const dynamic = "force-dynamic";
+
+async function fetchBook(bookId: string): Promise<BookDto | null> {
+  try {
+    return await apiFetch<BookDto>(`/books/${bookId}`);
+  } catch {
+    return null;
+  }
+}
+
+export default async function BookDetailPage({
+  params
+}: {
+  params: Promise<{ id: string }>;
+}) {
+  const { id } = await params;
+  const [book, libraries] = await Promise.all([
+    fetchBook(id),
+    fetchLibraries().catch(() => [] as { id: string; name: string }[])
+  ]);
+
+  if (!book) {
+    notFound();
+  }
+
+  const library = libraries.find(l => l.id === book.library_id);
+
+  return (
+    <>
+      <div className="breadcrumb">
+        <Link href="/books">← Back to books</Link>
+      </div>
+
+      <div className="book-detail">
+        <div className="book-detail-cover">
+          <Image
+            src={getBookCoverUrl(book.id)}
+            alt={`Cover of ${book.title}`}
+            width={300}
+            height={440}
+            className="detail-cover-image"
+            unoptimized
+          />
+        </div>
+
+        <div className="book-detail-info">
+          <h1>{book.title}</h1>
+          
+          {book.author && (
+            <p className="detail-author">by {book.author}</p>
+          )}
+
+          {book.series && (
+            <p className="detail-series">
+              {book.series}
+              {book.volume && <span className="volume">Volume {book.volume}</span>}
+            </p>
+          )}
+
+          <div className="detail-meta">
+            <div className="meta-row">
+              <span className="meta-label">Format:</span>
+              <span className={`book-kind ${book.kind}`}>{book.kind.toUpperCase()}</span>
+            </div>
+            
+            {book.language && (
+              <div className="meta-row">
+                <span className="meta-label">Language:</span>
+                <span>{book.language.toUpperCase()}</span>
+              </div>
+            )}
+            
+            {book.page_count && (
+              <div className="meta-row">
+                <span className="meta-label">Pages:</span>
+                <span>{book.page_count}</span>
+              </div>
+            )}
+
+            <div className="meta-row">
+              <span className="meta-label">Library:</span>
+              <span>{library?.name || book.library_id}</span>
+            </div>
+
+            <div className="meta-row">
+              <span className="meta-label">ID:</span>
+              <code className="book-id">{book.id}</code>
+            </div>
+          </div>
+        </div>
+      </div>
+    </>
+  );
+}