- Show which engine each task runs on (badge on active AND history rows; backend
  already tags t.engine) and an "● processing" badge on the engines card (new
  inflight/processing fields in /admin/api/engines).
- Image-gen advancement showed only "working…": poll() short-circuited to the
  synthesized task list whenever the primary had any in-flight request, dropping the
  engine's real step/total. Now it quick-polls the engine first (image/diffusers gen
  releases the GIL so it answers with real progress) and only falls back to the
  synthesized list when a GIL-bound text gen times out.
- Surface thermal cooldown on the task entry itself: _merge_engine_tasks marks tasks
  on a cooling engine with cooling/cooling_message (the row already renders it).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RdMufYvtTbtGDWsiZVoXce