perf: lazy-load heavy modal components with next/dynamic

Dynamic import EditBookForm, EditSeriesForm, MetadataSearchModal, and
ProwlarrSearchModal so their code is split into separate chunks and
only fetched when the user interacts with them.

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

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

@@ -2,11 +2,15 @@ import { fetchLibraries, getBookCoverUrl, BookDto, apiFetch, ReadingStatus } fro
 import { BookPreview } from "../../components/BookPreview";
 import { ConvertButton } from "../../components/ConvertButton";
 import { MarkBookReadButton } from "../../components/MarkBookReadButton";
-import { EditBookForm } from "../../components/EditBookForm";
+import nextDynamic from "next/dynamic";
 import { SafeHtml } from "../../components/SafeHtml";
 import { getServerTranslations } from "../../../lib/i18n/server";
 import Image from "next/image";
 import Link from "next/link";
+
+const EditBookForm = nextDynamic(
+  () => import("../../components/EditBookForm").then(m => m.EditBookForm)
+);
 import { notFound } from "next/navigation";
 
 export const dynamic = "force-dynamic";