perf(studio): virtualize the furniture table and throttle batch progress

- Render the table view through a virtualizer too, using a shared grid
  template so the sticky header and rows keep perfect column alignment
- Keep semantic table/row/cell elements while virtualizing
- Cap the batch item-details list to the latest 60 rows (newest first)
- Coalesce per-item progress events server-side (120ms throttle) in both
  the exact-import and clone SSE batch runners

src/app/api/admin/import/furni/batch/route.ts

@@ -117,6 +117,11 @@ export const POST = withAdmin(
 						});
 
 						try {
+							// Coalesce micro-step progress events to at most one per
+							// ~120ms per item so large imports don't flood the client
+							// (terminal states are always emitted by importSingleFurni
+							// and sent below).
+							let lastProgressSent = 0;
 							const result: ImportSingleResult = await importSingleFurni({
 								id: item.id ?? 0,
 								classname: item.classname,
@@ -131,6 +136,9 @@ export const POST = withAdmin(
 								nitroBaseUrl: source?.nitroBaseUrl,
 								iconBaseUrl: source?.iconBaseUrl,
 								onProgress: (status: string) => {
+									const now = Date.now();
+									if (now - lastProgressSent < 120) return;
+									lastProgressSent = now;
 									send({
 										type: "item_progress",
 										classname: item.classname,