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/events/[id]/page.tsx

@@ -12,6 +12,10 @@ import { EventPrizesManager } from "./event-prizes";
 import { EventRegistrations } from "./event-registrations";
 import { EventWinnersManager } from "./event-winners";
 
+// 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 EventDetailPage({
 	params,
 }: {

src/app/admin/events/create/page.tsx

@@ -5,6 +5,10 @@ import { db, WebsiteEventType } from "@/lib/db";
 import { canAccess, getAdminContext, PERMS } from "@/lib/permissions";
 import { EventForm } from "../event-form";
 
+// 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 CreateEventPage() {
 	const { session, permissions } = await getAdminContext();
 	if (!canAccess(permissions, PERMS.EVENTS_EDIT, session.user.rank)) {

src/app/admin/events/page.tsx

@@ -7,6 +7,10 @@ import { db, WebsiteEvent, WebsiteEventType } from "@/lib/db";
 import { PERMS } from "@/lib/permissions";
 import { EventsTable } from "./events-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 EventsPage({
 	params: paramsPromise,
 	searchParams,

src/app/admin/events/types/page.tsx

@@ -4,6 +4,10 @@ import { db, WebsiteEventType } from "@/lib/db";
 import { canAccess, getAdminContext, PERMS } from "@/lib/permissions";
 import { EventTypesManager } from "./event-types-manager";
 
+// 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 EventTypesPage() {
 	const { session, permissions } = await getAdminContext();
 	if (!canAccess(permissions, PERMS.EVENTS_EDIT, session.user.rank)) {