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/batch-regen/route.ts

@@ -4,6 +4,10 @@ import { eq } from "drizzle-orm";
 import { apiError } from "@/lib/api";
 import { withAdmin } from "@/lib/api-handler";
 import { db, ItemsBase } from "@/lib/db";
+import {
+	bundleExistsInDir,
+	bundleWritePathInDir,
+} from "@/lib/furni/bundle-file";
 import { PERMS } from "@/lib/permissions";
 import { getFurniAssetDirs } from "@/lib/services/furni-asset-dirs";
 import {
@@ -103,12 +107,12 @@ export const POST = withAdmin(
 							starIdx !== -1
 								? item.classname.substring(0, starIdx)
 								: item.classname;
-						const nitroPath = path.join(
-							/*turbopackIgnore: true*/ nitroDir,
-							`${baseClassname}.nitro`,
-						);
-
-						if (existsSync(/*turbopackIgnore: true*/ nitroPath)) {
+						if (
+							bundleExistsInDir(
+								/*turbopackIgnore: true*/ nitroDir,
+								baseClassname,
+							)
+						) {
 							skipped++;
 							send({
 								type: "regen_progress",
@@ -203,6 +207,10 @@ export const POST = withAdmin(
 								swfBuffer,
 								baseClassname,
 							);
+							const nitroPath = bundleWritePathInDir(
+								/*turbopackIgnore: true*/ nitroDir,
+								baseClassname,
+							);
 							await fs.writeFile(nitroPath, conversion.bundle);
 
 							// Build FurnitureData entry if missing