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/clone-import.test.ts

@@ -1,5 +1,5 @@
 // @vitest-environment node
-import { describe, expect, it, vi } from "vitest";
+import { beforeEach, describe, expect, it, vi } from "vitest";
 
 // biome-ignore lint/suspicious/noExplicitAny: test helper for mocking with arbitrary signatures
 type AnyFn = (...args: any[]) => any;
@@ -69,7 +69,11 @@ vi.mock("@/lib/db", () => ({
 	ItemsBase: { id: "id", itemName: "itemName" },
 }));
 
-import { cloneSingleFurni, parseFurnidata } from "./clone-import";
+import {
+	__resetItemsBaseAllocatorForTests,
+	cloneSingleFurni,
+	parseFurnidata,
+} from "./clone-import";
 
 const SOURCE = {
 	id: "s",
@@ -92,6 +96,10 @@ const ENTRY = {
 };
 
 describe("clone-import", () => {
+	beforeEach(() => {
+		__resetItemsBaseAllocatorForTests();
+	});
+
 	it("parseFurnidata normalizes room + wall items with itemType", () => {
 		const list = parseFurnidata({
 			roomitemtypes: { furnitype: [ENTRY] },