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/clone-import.ts

@@ -39,6 +39,8 @@ export interface CloneResult {
 	skipped?: boolean;
 	warnings: string[];
 	error?: string;
+	/** Set when `deferFurniData` is used so the caller can batch-write once. */
+	furniDataEntry?: { entry: Record<string, unknown>; itemType: string };
 }
 
 interface FurniType {
@@ -161,8 +163,11 @@ export async function cloneSingleFurni(params: {
 	source: CloneSource;
 	entry: SourceFurni;
 	onProgress?: (status: string) => void;
+	/** Skip the per-item FurnitureData.json write and return the entry instead,
+	 *  so batch callers can append everything in one lock + write cycle. */
+	deferFurniData?: boolean;
 }): Promise<CloneResult> {
-	const { source, entry, onProgress } = params;
+	const { source, entry, onProgress, deferFurniData } = params;
 	const { classname, itemType } = entry;
 	const warnings: string[] = [];
 
@@ -281,17 +286,19 @@ export async function cloneSingleFurni(params: {
 
 	// FurnitureData entry — reuse the source's furnitype object, with our id.
 	onProgress?.("writing_furnidata");
-	try {
-		await appendFurniEntry(
-			{ ...entry, id: newId } as Record<string, unknown>,
-			itemType,
-		);
-	} catch (err) {
-		logger.warn("[clone-import] FurnitureData append failed for", {
-			classname,
-			error: (err as Error).message,
-		});
-		warnings.push(`FurnitureData append failed: ${(err as Error).message}`);
+	const furniDataEntry = { ...entry, id: newId } as Record<string, unknown>;
+	if (deferFurniData) {
+		// Batch mode: the caller collects entries and appends them once at the end.
+	} else {
+		try {
+			await appendFurniEntry(furniDataEntry, itemType);
+		} catch (err) {
+			logger.warn("[clone-import] FurnitureData append failed for", {
+				classname,
+				error: (err as Error).message,
+			});
+			warnings.push(`FurnitureData append failed: ${(err as Error).message}`);
+		}
 	}
 
 	// Catalog entry (category sub-page + auto price), serialized id allocation.
@@ -312,7 +319,14 @@ export async function cloneSingleFurni(params: {
 		warnings.push(`catalog entry failed: ${(err as Error).message}`);
 	}
 
-	return { ok: true, classname, warnings };
+	return {
+		ok: true,
+		classname,
+		warnings,
+		furniDataEntry: deferFurniData
+			? { entry: furniDataEntry, itemType }
+			: undefined,
+	};
 }
 
 export async function getCloneList(params: {