Mark which stages are actually responsible for perceived realism

Add Test Bench: grid-inspect pipeline stages against real reference implementations

Add "Group by Layer" — cluster nodes by Senses/Brain/Face

Fix pasted-source bug: actually generate a pipeline instead of relabeling the demo

Ground the expert panel as Samantha: 5-failure-mode audit + tiering

Scaffold LAYER: pipeline node-graph viewer + 4D Avatar Expert