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/ads/[id]/page.tsx

@@ -9,6 +9,10 @@ import { db, WebsiteAds } from "@/lib/db";
 import { canAccess, getAdminContext, PERMS } from "@/lib/permissions";
 import { EditAdDeleteButton } from "../edit-ad-delete-button";
 
+// 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 EditAd({
 	params,
 }: {

src/app/admin/ads/new/page.tsx

@@ -5,6 +5,10 @@ import { createAd } from "@/actions/admin-ads";
 import { Button } from "@/components/ui/button";
 import { canAccess, getAdminContext, PERMS } from "@/lib/permissions";
 
+// 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 NewAd() {
 	const { session, permissions } = await getAdminContext();
 	if (!canAccess(permissions, PERMS.PAGES_EDIT, session.user.rank)) {

src/app/admin/ads/page.tsx

@@ -9,6 +9,10 @@ import { formatDate } from "@/lib/format-date";
 import { canAccess, getAdminContext, PERMS } from "@/lib/permissions";
 import { AdsTable } from "./ads-table";
 
+// 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 AdminAds() {
 	const { session, permissions } = await getAdminContext();
 	if (!canAccess(permissions, PERMS.PAGES_VIEW, session.user.rank)) {