feat(assets): choose furniture bundle ext via FURNI_BUNDLE_EXT

Bundle the remaining imaging hardening and the host/CI fixes from the
"Doe alles" pass into one release.

Furniture:
- Resolve the local bundle extension from FURNI_BUNDLE_EXT (".hab" default,
  ".nitro" for a stock Nitro client). The configured extension is written by
  imports/repairs and preferred on lookup; the other stays a legacy fallback.

Imaging:
- Avatar proxy sends s-maxage=86400 + stale-while-revalidate (300/3600 for the
  fallback path) so the edge can hold a render a day.
- Cloudflare cache rule now covers /api/imaging/ (verified MISS->HIT live).
- Document that bare /imaging is shadowed by the edge proxy to the renderer.

Ops/CI:
- docker-update.sh skips a CI-managed host (exit 0) instead of failing cron.
- ci-deploy.sh runs the cross-browser imaging gate (chromium+firefox+webkit)
  against the candidate before cutover; DEPLOY_SKIP_CROSS_BROWSER=1 as escape.
- scripts/imager-health-alert.sh alerts (Discord) on imager up/down transitions;
  runs from cron every 5 minutes.

Tests:
- Furniture bundle-ext resolver + FURNI_BUNDLE_EXT wiring.
- Imaging performance budget (bytes + warm latency).
- classifyDdos: /api/imaging/* stays in the api bucket.

src/app/imaging/route.ts

@@ -16,6 +16,20 @@ import {
 } from "@/lib/imager-upstream";
 import { resolveImagerBase } from "@/lib/runtime-asset-config";
 
+// Site-wide default imager endpoint. NOTE ON TOPOLOGY: in the current
+// production deployment the edge proxy (Traefik) fronts bare `/imaging` and
+// `/imaging/*` directly to the local pixinode renderer container, so this CMS
+// route is shadowed publicly and only answers when the CMS is reached directly
+// (local/dev, self-hosted installs without that proxy rule, or the deploy gate).
+// That is intentional: it keeps `habbo_imaging_url=/imaging` working without the
+// CMS in the hot path, and this route remains the correct fallback for any
+// install where no separate imager is proxied. Its behaviour is covered by
+// `src/lib/imaging-route.test.ts` and the CMS-only e2e (`e2e/imaging/cms-imaging.spec.ts`).
+//
+// It differs from the sibling `/api/imaging/avatar` route in that it also
+// transcodes PNG renders to WebP/AVIF (`?format=`) and is cached on disk per
+// (figure, variant).
+
 type AvatarFormat = "png" | "webp" | "avif";
 type TranscodeFormat = Exclude<AvatarFormat, "png">;