refactor: separate Scene controls from playback and project operations

docs/CODE-BOUNDARIES.md

@@ -320,3 +320,10 @@ cache and sampling operations, continuous-render owner and regional briefing
 service. Pure math, utility layout and vision helpers have explicit exports.
 Disposal releases subscriptions and pending work; portal moves preserve the
 original Display groups, independent scroll positions and current focus owner.
+
+## Scene controls
+
+`ui/scenes` owns Scene panel input, project/shot rows, playback button and runtime
+presentation. It receives project reads and explicit actions, with no imports of
+the director, source modules, camera engine or storage. Replacement and disposal
+release listeners; pending action feedback is limited to its current owner.