feat(catalog): store furniture bundles as .hab instead of .nitro

Every bundle the CMS writes — upload, clone, sync, repair and the pet /
effect / figure importers — now lands as `<classname>.hab`, the extension
this deployment's renderer asks for. `.hab` and `.nitro` are the same
container, so an upload of either extension is accepted.

Resolution goes through one module, src/lib/furni/bundle-file.ts, so
nothing has to know the extension twice. Every existence check probes
`.hab` first and falls back to `.nitro`: the on-disk asset set is still
predominantly `.nitro`, and without the fallback Studio would report every
imported item as missing and the cleanup scan would classify 18k live
bundles as fake leftovers. Downloads are unchanged — Habbo's CDN and every
configured clone source still serve `.nitro`, so the conversion happens on
write, not on request.

Deliberately unchanged: the staged-attachment store in furni-attachment.ts
keys on a UUID and never reaches the client, so renaming it would break
in-flight recovery jobs.

Adds scripts/migrate-nitro-to-hab.ts to rename the existing asset set. It
refuses to run without --dry-run or --yes, never overwrites an existing
.hab, never deletes, and is idempotent.

Note: renderer-config.json lives outside this repo and was patched to
.hab separately; that file is served with a 30-day max-age, so returning
clients need a cms-client cache purge to pick the change up.

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

@@ -5,6 +5,10 @@ import { invalidateCatalogTotals } from "@/features/catalog/server/catalog-total
 import { apiError, apiOk } from "@/lib/api";
 import { withAdmin } from "@/lib/api-handler";
 import { db, ItemsBase, queryRows } from "@/lib/db";
+import {
+	bundleExistsInDir,
+	bundleWritePathInDir,
+} from "@/lib/furni/bundle-file";
 import { isSafeAssetName, normalizeClassname } from "@/lib/furni/classname";
 import { localFurnitureStatus } from "@/lib/furni/local-presence";
 import { PERMS } from "@/lib/permissions";
@@ -723,13 +727,16 @@ export const PATCH = withAdmin(
 			const starIdx = normalised.indexOf("*");
 			const baseClassname =
 				starIdx !== -1 ? normalised.substring(0, starIdx) : normalised;
-			const nitroPath = path.join(
+			// Regeneration writes `.hab`; a legacy `.nitro` counts as present too.
+			const nitroPath = bundleWritePathInDir(
 				/*turbopackIgnore: true*/ nitroDir,
-				`${baseClassname}.nitro`,
+				baseClassname,
 			);
 
-			// Skip if .nitro already exists
-			if (existsSync(/*turbopackIgnore: true*/ nitroPath)) {
+			// Skip if a bundle already exists (`.hab` or legacy `.nitro`).
+			if (
+				bundleExistsInDir(/*turbopackIgnore: true*/ nitroDir, baseClassname)
+			) {
 				results.push({
 					classname: item.classname,
 					ok: true,