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.

e2e/imaging/performance-budget.spec.ts

@@ -0,0 +1,39 @@
+import { expect, test } from "@playwright/test";
+import { avatarPath } from "./imaging-target";
+
+// Lightweight size/latency budget for the avatar path. The endpoint spec checks
+// correctness; this one catches a regression that keeps the image correct but
+// makes it oversized or slow — e.g. losing the disk/edge cache and re-encoding
+// (or re-rendering) on every hit. Budgets are deliberately loose: they should
+// flag a real regression, not a cold cache or a slow CI network.
+const STATIC_MAX_BYTES = 64 * 1024;
+const ANIMATED_MAX_BYTES = 512 * 1024;
+const WARM_MAX_MS = 3000;
+
+test("the static avatar stays inside its byte budget", async ({ request }) => {
+	const response = await request.get(avatarPath({ img_format: "png" }));
+	expect(response.status()).toBe(200);
+	expect((await response.body()).length).toBeLessThanOrEqual(STATIC_MAX_BYTES);
+});
+
+test("the animated avatar stays inside its byte budget", async ({
+	request,
+}) => {
+	const response = await request.get(
+		avatarPath({ img_format: "apng", effect: "14" }),
+	);
+	expect(response.status()).toBe(200);
+	expect((await response.body()).length).toBeLessThanOrEqual(
+		ANIMATED_MAX_BYTES,
+	);
+});
+
+test("a warm avatar request is served quickly", async ({ request }) => {
+	const path = avatarPath({ img_format: "png" });
+	await request.get(path); // warm the disk and edge caches
+	const started = Date.now();
+	const response = await request.get(path);
+	const elapsed = Date.now() - started;
+	expect([200, 304]).toContain(response.status());
+	expect(elapsed).toBeLessThan(WARM_MAX_MS);
+});