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/InspectorPanel.cpp

@@ -215,6 +215,17 @@ void InspectorPanel::Draw(const EditorContext& ctx, entt::entity selected)
     {
         if (ComponentHeader("Transform", nullptr, false, nullptr))
         {
+            // 父级提示（UE Details 语义：此处编辑的是 Relative 值）
+            if (ctx.scene) {
+                const Engine::ECS::Entity p = ctx.scene->GetParent(selected);
+                if (p != entt::null) {
+                    std::string pname = "(unnamed)";
+                    if (const auto* n = reg.try_get<Engine::ECS::NameComponent>(p)) {
+                        pname = n->name;
+                    }
+                    ImGui::TextDisabled("parent: %s", pname.c_str());
+                }
+            }
             glm::vec3 pos = t->GetPosition();
             if (DragVec3Row("position", pos, 0.05f))
             {