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/AssetBrowserPanel.cpp

@@ -85,7 +85,7 @@ namespace {
 
 void AssetBrowserPanel::Draw(const EditorContext& ctx)
 {
-    if (!ImGui::Begin("Asset Browser"))
+    if (!ImGui::Begin("Content Browser"))
     {
         ImGui::End();
         return;