perf(import): adjustable concurrency and skip redundant SWF downloads

Raise batch concurrency (furni 3->12, clone 10->12) with a Speed control next to Translate. Skip the SWF download when a .nitro bundle already exists on disk (color variants share the base nitro), and stop flagging that as a failed download.

src/lib/services/furni-import.ts

@@ -711,7 +711,13 @@ export async function importSingleFurni(params: {
 					iconFailure = detail;
 					warnings.push(`Icon download failed: ${detail}`);
 				}),
-		params.providedNitro || (params.preserveAssets && existsSync(nitroPath))
+		// Skip the SWF download entirely when a .nitro bundle already exists on
+		// disk — this happens for colour variants that share the base classname's
+		// nitro file. The SWF is only used for Nitro conversion (not needed) and
+		// icon extraction (the nitro bundle is used as a fallback for that below).
+		existsSync(/*turbopackIgnore: true*/ nitroPath) ||
+		params.providedNitro ||
+		(params.preserveAssets && existsSync(nitroPath))
 			? Promise.resolve(false)
 			: (preservingExisting || params.preserveAssets) && existsSync(swfPath)
 				? Promise.resolve(true)
@@ -766,6 +772,7 @@ export async function importSingleFurni(params: {
 		!swfOk &&
 		!nitroDownloadOk &&
 		!params.providedNitro &&
+		!existsSync(/*turbopackIgnore: true*/ nitroPath) &&
 		!(params.preserveAssets && existsSync(nitroPath))
 	)
 		warnings.push(`SWF download failed: ${swfFailure || "unknown cause"}`);