perf: enable source-specific asset downloads and make nitro/icon URLs optional

Import improvements:
- importSingleFurni now accepts sourceSwfBaseUrl, nitroBaseUrl, iconBaseUrl
  params to try source-specific asset downloads before falling back to
  the official Habbo CDN (images.habbo.com)
- Source-specific URL cascade:
  1. Try sourceSwfBaseUrl/hof_furni/{rev}/{name}.swf
  2. Try sourceNitroBaseUrl/{name}.nitro (pre-made nitro bundles)
  3. Fallback to images.habbo.com/dcr/hof_furni/{rev}/{name}.swf
- Same fallback chain for icon downloads
- Clone sources can now have empty nitroBaseUrl/iconBaseUrl (retro
  hotels without nitro support)
- Added VirtualCity source (verified SWF downloads via virtualc.nl/dcr)
- Added sourceSwfBaseUrl field to CloneSource interface
- Both batch and single import routes pass source params through
- Clone POST route accepts sourceSwfBaseUrl, makes nitro/icon optional
- Nitro fallback download tries .nitro files before SWF conversion

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

@@ -2,6 +2,7 @@ import { withAdmin } from "@/lib/api-handler";
 import { apiError } from "@/lib/api-response";
 import { PERMS } from "@/lib/permissions";
 import { logAudit } from "@/lib/services/audit";
+import { getSource } from "@/lib/services/clone-sources";
 import { appendFurniEntriesBatch } from "@/lib/services/furni-data";
 import {
 	ensureDirectories,
@@ -31,9 +32,16 @@ export const POST = withAdmin(
 		const body = await request.json();
 		const rawItems: BatchItem[] = body.items || [];
 		const concurrency = Math.min(Math.max(body.concurrency || 3, 1), 5);
+		const sourceId: string | undefined = body.sourceId;
 
 		if (rawItems.length === 0) return apiError("No items to import", 400);
 
+		// Look up clone source for SWF/nitro/icon URL fallbacks
+		let source: Awaited<ReturnType<typeof getSource>> | null = null;
+		if (sourceId) {
+			source = await getSource(sourceId);
+		}
+
 		// Deduplicate by (spriteId, classname) to avoid concurrent INSERT races on
 		// items_base.id when the same item is listed twice in the request body.
 		const seen = new Set<string>();
@@ -94,6 +102,9 @@ export const POST = withAdmin(
 								revision: item.revision ?? 0,
 								category: item.category ?? "unknown",
 								skipFurniDataWrite: true,
+								sourceSwfBaseUrl: source?.sourceSwfBaseUrl,
+								nitroBaseUrl: source?.nitroBaseUrl,
+								iconBaseUrl: source?.iconBaseUrl,
 								onProgress: (status: string) => {
 									send({
 										type: "item_progress",