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/mod/actions/page.tsx

@@ -2,6 +2,10 @@ import { ModActionsClient } from "@/app/admin/moderation/actions/mod-actions-cli
 import { requireModPermission } from "@/lib/admin/guard";
 import { 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 ModQuickActionsPage() {
 	await requireModPermission([PERMS.MOD_ACTIONS, PERMS.MODERATION_EDIT]);