scenario-form.js — full rewrite:
- Full-screen modal (backdrop + content, 800px max-width)
- Services dropdown (GET /api/services, cached)
- Operations dropdown (GET /api/operations/{svcId}, cached)
- output field for create steps
- instance_ref dropdown (previous outputs) + explicit instance_uid
- [↑][↓] reorder buttons
- Auto-load operations on service change
index.html — modal CSS (#scenario-modal, .modal-backdrop, .modal-content)