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/clone/route.ts

@@ -76,8 +76,15 @@ export const POST = withAdmin(
 	{ permission: PERMS.ASSETS_IMPORT },
 	async (request, ctx) => {
 		const body = await request.json();
-		const { name, furnidataUrl, nitroBaseUrl, iconBaseUrl, hotel, id } =
-			body as Record<string, string>;
+		const {
+			name,
+			furnidataUrl,
+			nitroBaseUrl,
+			iconBaseUrl,
+			hotel,
+			id,
+			sourceSwfBaseUrl,
+		} = body as Record<string, string>;
 
 		const isHttps = (u: string) => {
 			try {
@@ -89,22 +96,21 @@ export const POST = withAdmin(
 
 		if (!name?.trim()) return apiError("name is required", 400);
 		if (!furnidataUrl?.trim()) return apiError("furnidataUrl is required", 400);
-		if (!nitroBaseUrl?.trim()) return apiError("nitroBaseUrl is required", 400);
-		if (!iconBaseUrl?.trim()) return apiError("iconBaseUrl is required", 400);
-		if (
-			!isHttps(furnidataUrl) ||
-			!isHttps(nitroBaseUrl) ||
-			!isHttps(iconBaseUrl)
-		)
-			return apiError("Source URLs must be valid https:// URLs", 400);
+
+		const normalized = (u: string | undefined) =>
+			(u ?? "").trim().replace(/\/+$/, "");
+
+		if (!isHttps(furnidataUrl))
+			return apiError("furnidataUrl must be a valid https:// URL", 400);
 
 		const entry = await upsertSource({
 			id,
 			name,
 			furnidataUrl,
-			nitroBaseUrl,
-			iconBaseUrl,
+			nitroBaseUrl: normalized(nitroBaseUrl),
+			iconBaseUrl: normalized(iconBaseUrl),
 			hotel: hotel ?? "",
+			sourceSwfBaseUrl: normalized(sourceSwfBaseUrl),
 		});
 
 		logAudit({