docs: Document stub/not-implemented methods in resources module

Fixed discrepancies between source code and documentation:
- AsyncLoader: Document Initialize() ignores workerThreadCount, Submit() doesn't do actual async loading, Update() is stub
- ResourceManager: Document UnloadUnused() and ReloadResource() are stubs
- ResourceCache: Document OnZeroRefCount() and Flush() are stubs
- ResourceDependencyGraph: Document TopologicalSort() returns empty (stub)
- ResourceFileSystem: Document GetResourceInfo() doesn't fill modifiedTime, EnumerateResources() is stub
- FileArchive: Document Enumerate() is stub
- ResourcePackageBuilder: Document AddDirectory() is stub
- ImportSettings: Document LoadFromJSON/SaveToJSON are stubs
- TextureImportSettings/MeshImportSettings: Document JSON methods are stubs
- TextureLoader/MeshLoader/MaterialLoader/ShaderLoader/AudioLoader: Document GetDefaultSettings() returns nullptr
- AudioLoader: Document ParseWAVData() is stub, Load() doesn't parse WAV headers
- ShaderLoader: Document DetectShaderType/ParseShaderSource are stubs
- MaterialLoader: Document ParseMaterialData() is stub
- Texture: Document Create() mipLevels=0 behavior, GenerateMipmaps() returns false
- Mesh: Document MeshLoader::Load() is example only
- IResourceLoader: Document GetDefaultSettings() returns nullptr for all loaders

docs/api/math/color/color.md

@@ -17,6 +17,11 @@ struct Color {
 };
 ```
 
+## 构造函数
+
+- `Color()` - 默认构造，初始化为白色 (1, 1, 1, 1)
+- `constexpr Color(float r, float g, float b, float a = 1.0f)` - 从 RGBA 分量构造
+
 ## 静态工厂方法
 
 | 方法 | 返回值 | 描述 |