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/lib/services/import/core/sse-batch.ts

@@ -17,6 +17,13 @@ export interface RunSseBatchOptions<T> {
 		index: number,
 		report: (status: string) => void,
 	) => Promise<SseWorkerResult>;
+	/**
+	 * Optional finalizer run once after every item settles, before
+	 * batch_complete is emitted. Lets callers flush deferred work (e.g. a single
+	 * FurnitureData.json write) instead of doing it per item. Failures are
+	 * surfaced as an `error` event without aborting the stream.
+	 */
+	flush?: () => Promise<void>;
 }
 
 /**
@@ -25,8 +32,8 @@ export interface RunSseBatchOptions<T> {
  * Stops starting new chunks when `signal` aborts or the client cancels the stream.
  */
 export function runSseBatch<T>(opts: RunSseBatchOptions<T>): Response {
-	const { items, labelOf, worker, signal } = opts;
-	const concurrency = Math.min(Math.max(opts.concurrency || 3, 1), 5);
+	const { items, labelOf, worker, signal, flush } = opts;
+	const concurrency = Math.min(Math.max(opts.concurrency || 3, 1), 10);
 	const encoder = new TextEncoder();
 	const ac = new AbortController();
 
@@ -113,6 +120,17 @@ export function runSseBatch<T>(opts: RunSseBatchOptions<T>): Response {
 				);
 			}
 
+			if (flush) {
+				try {
+					await flush();
+				} catch (err) {
+					send({
+						type: "error",
+						message: (err as Error).message,
+					});
+				}
+			}
+
 			if (!ac.signal.aborted) {
 				send({
 					type: "batch_complete",