perf: throttle localized furnidata build to avoid 100% CPU spikes

Lower LibreTranslate concurrency to 2 and yield the event loop between
languages so the 13x deep-clone + stringify loop no longer pins a core
continuously. The build is also already opt-in (off by default on import).

src/lib/services/furni-data-i18n.ts

@@ -186,7 +186,15 @@ async function translateWithLibre(
 }
 
 const LIBRE_BATCH_SIZE = 48;
-const LIBRE_CONCURRENCY = 4;
+// Kept low on purpose: the build already pegs a core with the synchronous
+// deep-clone + stringify of the 100k+ entry master per language, so we avoid
+// spreading onto multiple cores at once.
+const LIBRE_CONCURRENCY = 2;
+// Breathing room between languages so the event loop (and other CMS requests)
+// is never monopolised by the build loop.
+const BUILD_YIELD_MS = 150;
+
+const sleep = (ms: number) => new Promise((r) => setTimeout(r, ms));
 
 /**
  * Translate many texts in one go using LibreTranslate's array API
@@ -463,6 +471,12 @@ export async function buildLocalizedFurniDataFiles(
 
 		for (const { lang, hotel, map } of maps) {
 			try {
+				// Yield before each language (except the first) so a long build
+				// never pins the CPU continuously and the server stays responsive.
+				if (results.length > 0) {
+					await new Promise((r) => setImmediate(r));
+					await sleep(BUILD_YIELD_MS);
+				}
 				const cloned = cloneFurniData(
 					master as unknown as Record<string, unknown>,
 				);