refactor: reorganize Resources module into Core/Asset, Core/IO and Resources subdirectories

- Split core resource architecture into Core/Asset/ (IResource, ResourceManager, ResourceCache, etc.)
- Moved IO layer into Core/IO/ (IResourceLoader, ResourceFileSystem, etc.)
- Reorganized concrete resource types into Resources/{Texture,Mesh,Material,Shader,AudioClip}/
- Updated all include paths from relative to <XCEngine/...> format
- Fixed circular dependency in Material.h (removed unnecessary ResourceManager.h include)
- Fixed malformed include syntax in ResourceManager.h and AsyncLoader.h
- Fixed glad.h path issues in CMakeLists.txt

engine/src/Resources/Mesh/MeshImportSettings.cpp

@@ -0,0 +1,23 @@
+#include <XCEngine/Resources/MeshImportSettings.h>
+
+namespace XCEngine {
+namespace Resources {
+
+MeshImportSettings::MeshImportSettings() = default;
+
+MeshImportSettings::~MeshImportSettings() = default;
+
+Core::UniqueRef<ImportSettings> MeshImportSettings::Clone() const {
+    return Core::UniqueRef<ImportSettings>(new MeshImportSettings(*this));
+}
+
+bool MeshImportSettings::LoadFromJSON(const Containers::String& json) {
+    return false;
+}
+
+Containers::String MeshImportSettings::SaveToJSON() const {
+    return Containers::String();
+}
+
+} // namespace Resources
+} // namespace XCEngine