feat: speed up admin clone import and enable Cache Components

- Clone import: defer FurnitureData.json writes and append all entries in a
  single batched write instead of one read-modify-write per item, removing
  the main serialization bottleneck for large batches.
- Clone import: raise SSE batch concurrency cap from 5 to 10 and bump the
  clone client/route default from 2 to 6.
- Add a flush hook to runSseBatch so callers can batch deferred work before
  batch_complete is emitted, and surface flush errors as an error event.
- Enable Next.js Cache Components (instant: false opt-out) and silence the
  related build warnings in next.config.ts.
- Switch isomorphic-dompurify to dompurify and refresh dependencies.

src/app/admin/import/clone/import-clone-client.tsx

@@ -454,7 +454,7 @@ function FurniGrid({ source }: FurniGridProps) {
 				{
 					sourceId: source.id,
 					classnames: toClone.map((it) => it.classname),
-					concurrency: 2,
+					concurrency: 6,
 				},
 				(classname) => {
 					done++;
@@ -545,7 +545,7 @@ function FurniGrid({ source }: FurniGridProps) {
 				const chunk = names.slice(i, i + CHUNK);
 				await runSseImport(
 					"/api/admin/import/clone/batch",
-					{ sourceId: source.id, classnames: chunk, concurrency: 2 },
+					{ sourceId: source.id, classnames: chunk, concurrency: 6 },
 					(classname) => {
 						done++;
 						markDone(classname);

src/app/admin/import/clone/page.tsx

@@ -2,6 +2,10 @@ import { redirect } from "next/navigation";
 import { canAccess, getAdminContext, PERMS } from "@/lib/permissions";
 import { ImportCloneClient } from "./import-clone-client";
 
+// TODO: Cache Components adoption. Refactor this route so this opt-out can be removed.
+// See: https://nextjs.org/docs/app/guides/migrating-to-cache-components
+export const instant = false;
+
 export default async function ImportClonePage(_props: {
 	params: Promise<{ locale: string }>;
 }) {