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.

README.md

@@ -583,7 +583,7 @@ URLs look like `https://<hotel>/imaging/avatarimage?figure=hd-180-1.ch-210-66&im
 ### Requirements (host)
 
 - Docker (daemon with `build.network: host`, same as the CMS build — this host disables Docker iptables).
-- An nginx that serves `/gamedata/` (FigureData/FigureMap/EffectMap…) and `/gamedata/bundled` (`.nitro` assets) over HTTP so the renderer can fetch them. The compose file points at `host.docker.internal:8081`.
+- An nginx that serves `/gamedata/` (FigureData/FigureMap/EffectMap…) and `/gamedata/bundled` (furniture bundle assets — `.hab`, the extension imports write and this deployment's client requests, plus any legacy `.nitro` still on disk) over HTTP so the renderer can fetch them. The compose file points at `host.docker.internal:8081`.
 
 ### Configuration — `/docker/Polaris-imager/.env`