perf(import): parallelize ID allocation and raise clone concurrency to 10

Replace the serialized SELECT MAX + INSERT id-allocation chains for
items_base and catalog_items with a lazy-seeded in-process counter so
concurrent clone workers no longer queue on a global lock per item.
Re-seeds after 60s idle to avoid colliding with externally added rows.
Raise the clone import concurrency default from 6 to the batch cap of 10.

src/lib/services/upload-import.test.ts

@@ -82,12 +82,16 @@ vi.mock("@/lib/services/swf/nitro-builder", () => ({
 	parseNitroBundle: vi.fn(() => ({ json: { xdim: 1, ydim: 1 } })),
 }));
 
-import { uploadSingleFurni } from "./upload-import";
+import {
+	__resetUploadItemsBaseAllocatorForTests,
+	uploadSingleFurni,
+} from "./upload-import";
 
 describe("uploadSingleFurni live asset mirrors", () => {
 	let tempDir: string;
 
 	beforeEach(async () => {
+		__resetUploadItemsBaseAllocatorForTests();
 		tempDir = await fs.mkdtemp(path.join(os.tmpdir(), "upload-furni-"));
 		assetTargets.swfDir = path.join(tempDir, "cms", "swf");
 		assetTargets.iconDir = path.join(tempDir, "cms", "icons");