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/MeshLoader.cpp

@@ -0,0 +1,64 @@
+#include "Resources/MeshLoader.h"
+#include "Resources/ResourceManager.h"
+
+namespace XCEngine {
+namespace Resources {
+
+MeshLoader::MeshLoader() = default;
+MeshLoader::~MeshLoader() = default;
+
+Containers::Array<Containers::String> MeshLoader::GetSupportedExtensions() const {
+    Containers::Array<Containers::String> extensions;
+    extensions.PushBack(Containers::String("fbx"));
+    extensions.PushBack(Containers::String("obj"));
+    extensions.PushBack(Containers::String("gltf"));
+    extensions.PushBack(Containers::String("glb"));
+    extensions.PushBack(Containers::String("dae"));
+    extensions.PushBack(Containers::String("stl"));
+    return extensions;
+}
+
+bool MeshLoader::CanLoad(const Containers::String& path) const {
+    Containers::String ext = GetExtension(path);
+    ext.ToLower();
+    
+    return ext == "fbx" || ext == "obj" || ext == "gltf" || 
+           ext == "glb" || ext == "dae" || ext == "stl";
+}
+
+LoadResult MeshLoader::Load(const Containers::String& path, const ImportSettings* settings) {
+    (void)settings;
+    
+    Containers::String ext = GetExtension(path);
+    ext.ToLower();
+    
+    if (!CanLoad(path)) {
+        return LoadResult(Containers::String("Unsupported mesh format: ") + ext);
+    }
+    
+    Containers::Array<Core::uint8> fileData = ReadFileData(path);
+    if (fileData.Empty()) {
+        return LoadResult(Containers::String("Failed to read file: ") + path);
+    }
+    
+    auto* mesh = new Mesh();
+    
+    IResource::ConstructParams params;
+    params.name = path;
+    params.path = path;
+    params.guid = ResourceGUID::Generate(path);
+    params.memorySize = fileData.Size();
+    
+    mesh->Initialize(params);
+    
+    return LoadResult(mesh);
+}
+
+ImportSettings* MeshLoader::GetDefaultSettings() const {
+    return nullptr;
+}
+
+REGISTER_RESOURCE_LOADER(MeshLoader);
+
+} // namespace Resources
+} // namespace XCEngine