Editor: rework default layout to UE5 arrangement

Panels renamed to UE semantics (docking identity change): Hierarchy ->
Outliner, Inspector -> Details, Asset Browser -> Content Browser.

Default DockBuilder layout now matches UE5 factory layout: Details
docked right (full height), Content Browser docked bottom spanning
left+center, Outliner top-left, Viewport center with Stats as a
side tab.

Legacy imgui.ini (old window names, no new names) is removed once at
Init so the new default rebuilds cleanly; fresh or new-style ini is
untouched.

App/editor/HierarchyPanel.cpp

@@ -146,7 +146,7 @@ namespace {
 
 void HierarchyPanel::Draw(const EditorContext& ctx, entt::entity& selected)
 {
-    ImGui::Begin("Hierarchy");
+    ImGui::Begin("Outliner");
 
     // 工具栏：创建实体（在遍历之前，不修改遍历中的注册表结构）
     if (ImGui::Button("+ Create Entity"))