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.

scripts/ci-deploy.sh

@@ -410,7 +410,10 @@ if [ -n "$(git status --porcelain --untracked-files=normal)" ]; then
 fi
 
 pnpm install --frozen-lockfile
-pnpm exec playwright install chromium
+# All three engines are needed: the chromium gate below plus the cross-browser
+# imaging gate just before cutover. Idempotent — already-installed engines in
+# PLAYWRIGHT_BROWSERS_PATH are detected and skipped.
+pnpm exec playwright install chromium firefox webkit
 
 echo "Building $image"
 # No --network=host: BuildKit only grants it via --allow=network.host, and the
@@ -536,6 +539,18 @@ if [ "$blue_green" -eq 1 ]; then
   node scripts/verify-deployed-release.mjs "http://127.0.0.1:$new_port/api/health" "$sha"
   PLAYWRIGHT_BASE_URL="http://127.0.0.1:$new_port" pnpm test:e2e
 
+  # 4b. Cross-browser imaging gate. The chromium suite above proves the
+  #     candidate serves the right bytes; this proves every bundled engine can
+  #     actually decode the render. The webkit path is the one that historically
+  #     broke (CSP upgrade-insecure-requests + animated PNG), and a regression
+  #     there must never reach live. Set DEPLOY_SKIP_CROSS_BROWSER=1 only to get
+  #     a release out in an emergency.
+  if [ "${DEPLOY_SKIP_CROSS_BROWSER:-0}" = "1" ]; then
+    echo "WARNING: cross-browser imaging gate skipped (DEPLOY_SKIP_CROSS_BROWSER=1)" >&2
+  else
+    PLAYWRIGHT_BASE_URL="http://127.0.0.1:$new_port" pnpm test:imaging
+  fi
+
   # 5. Het enige onomkeerbare moment: vanaf hier wijst nginx naar de kandidaat.
   cutover_started=1
   switch_upstream "$new_port"
@@ -569,6 +584,11 @@ else
   healthy 3002
   node scripts/verify-deployed-release.mjs http://127.0.0.1:3002/api/health "$sha"
   PLAYWRIGHT_BASE_URL=http://127.0.0.1:3002 pnpm test:e2e
+  if [ "${DEPLOY_SKIP_CROSS_BROWSER:-0}" = "1" ]; then
+    echo "WARNING: cross-browser imaging gate skipped (DEPLOY_SKIP_CROSS_BROWSER=1)" >&2
+  else
+    PLAYWRIGHT_BASE_URL=http://127.0.0.1:3002 pnpm test:imaging
+  fi
   verified_image="$(docker inspect --format '{{.Image}}' epicnext-cms-app)"
 fi
 docker tag "$verified_image" "epicnext-cms:verified-$sha"