Puts the sublayer stack directly under the edit-target combo in the Scene
Hierarchy, so muting and reordering no longer require switching to the
separate Stage Editor window.
Each row mirrors StageEditorPanel: drag handle with drag-drop reorder, dirty
indicator, name (dimmed when muted, [RL] badge for render-layer sublayers),
edit-target checkbox and mute checkbox. Adds dedicated up/down chevron icon
buttons for reordering, which the Stage Editor only exposed as context-menu
items. Reorder goes through the existing LayerReorderCommand so it is undoable;
mute calls LayerManager directly, matching current app-wide behaviour.
New Icon::ChevronUp / ChevronDown with matching SVGs.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
