Replaces cmd_queue-based cancel polling with a shared mp.Event.
Fixes two issues:
- Loading a new model while generating no longer hangs (cancel is instant)
- Subprocess shuts down cleanly after explicit stop generation
Inference now runs in a persistent subprocess, solving the same
transformers version-switching problem that was fixed for training.
The subprocess stays alive between requests (model in GPU memory)
and is only restarted when switching transformers versions.
New files:
- core/inference/worker.py: subprocess entry point with command loop
- core/inference/orchestrator.py: parent-side proxy with same API
Modified:
- core/inference/__init__.py: exports orchestrator as default backend
- routes/inference.py: removed in-process ensure_transformers_version()
