feat: parent-child transform hierarchy (UE Actor attach semantics)

- TransformComponent TRS = local (relative to parent); cached world SRT
  composed hierarchically (parent pos/rot/scale, no matrix decomposition
  shear under non-uniform parent scale)
- HierarchyComponent (parent + children, lazily attached); Scene::
  SetParent (keepWorld, cycle-safe) / GetParent / IsDescendantOf /
  SetWorldPose (world->local inverse, used by physics writeback & gizmo)
- UpdateTransforms: DFS from roots, recompose only dirty-or-dirty-
  ancestor subtrees (parents before children)
- DestroyEntity: descendants buried with parent (UE cascade)
- Serialization v2: optional Parent uuid key, two-pass relink on load
- Hierarchy panel: tree view, drag-drop reparent / drop-to-root detach,
  Create Child / Detach context menu; Inspector shows parent name
- Consumers moved to world-space reads: lights, camera pos, physics
  bodies/characters/joints/collider baking, gizmo, F-focus, AlignTo

App/editor/HierarchyPanel.h

@@ -1,8 +1,9 @@
 //
-// HierarchyPanel：实体列表面板。
+// HierarchyPanel：实体层级树面板。
 //
-// 点击选中（写 Editor 的选中状态）、工具栏创建实体、右键删除
-//（延迟销毁，帧尾 flush，遍历安全）。每项尾缀显示组件构成徽标。
+// 树形展示父子层级（UE Outliner）、点击选中、拖拽改父/拖到空白挂根
+//（keepWorld）、右键 Create Child / Detach / Delete（级联随葬，帧尾
+// flush，遍历安全）。每项尾缀显示组件构成徽标。
 //
 
 #ifndef HELLOVULKAN_HIERARCHYPANEL_H