Refactor new editor boundaries and test ownership

new_editor/app/Features/Project/ProjectBrowserModel.cpp

@@ -1,8 +1,6 @@
 #include "ProjectBrowserModel.h"
 #include "ProjectBrowserModelInternal.h"
 
-#include "Internal/StringEncoding.h"
-
 #include <fstream>
 
 namespace XCEngine::UI::Editor::App {
@@ -238,9 +236,9 @@ bool ProjectBrowserModel::CreateMaterial(
         }
 
         std::filesystem::path requestedPath =
-            App::Internal::Utf8ToWide(trimmedName);
+            BuildPathFromUtf8(trimmedName);
         if (!requestedPath.has_extension()) {
-            requestedPath += L".mat";
+            requestedPath.replace_extension(".mat");
         }
 
         const std::filesystem::path materialPath =
@@ -317,7 +315,7 @@ bool ProjectBrowserModel::RenameItem(
         }
 
         const std::filesystem::path destinationPath =
-            (sourcePath->parent_path() / App::Internal::Utf8ToWide(targetName))
+            (sourcePath->parent_path() / BuildPathFromUtf8(targetName))
                 .lexically_normal();
         const std::string destinationItemId =
             BuildRelativeItemId(destinationPath, m_assetsRootPath);