feat: Implement resource system Phase 2 - Concrete resource types

- Add Material class with shader/texture bindings and property system
- Add MaterialLoader for .mat/.json format
- Add Shader class (Vertex/Fragment/Geometry/Compute)
- Add ShaderLoader for .vert/.frag/.glsl/.hlsl
- Add AudioClip class (WAV/OGG/MP3/FLAC support)
- Add AudioLoader for audio files
- Add Texture/Mesh classes and loaders (from design doc)
- Fix HashMap iterator and String API usage
- Fix Mutex compatibility with std::lock_guard
- Update CMakeLists.txt with new resource files
- All tests pass: 11 Resources + 51 Containers

engine/include/XCEngine/Containers/HashMap.h

@@ -237,7 +237,10 @@ bool HashMap<Key, Value>::Erase(const Key& key) {
     auto it = FindInBucket(bucket, key);
     if (it != bucket.pairs.end()) {
         size_t index = it - bucket.pairs.begin();
-        bucket.pairs[index] = bucket.pairs.Back();
+        
+        if (index != bucket.pairs.Size() - 1) {
+            bucket.pairs[index] = std::move(bucket.pairs.Back());
+        }
         bucket.pairs.PopBack();
         --m_size;
         return true;