Refactor pipeline state and render output abstractions

- Replace old pipeline enums/structs with new strongly-typed PipelineState and enums (ZTest, ZWrite, Cull, Blend, ColorWriteMask)
- Redesign pipeline keying: introduce 128-bit GraphicsPipelineKey, MaterialPipelineKey, and PassPipelineKey for robust PSO caching
- Replace IRenderTargetStrategy with IRenderOutput; add SwapChainRenderOutput and TextureRenderOutput
- Update renderer and window code to use new render output abstraction and handle viewport/scissor updates
- Make ShaderPass a readonly struct and Shader a struct; use ID-based pass lookup for efficiency
- Materials now support per-pass pipeline overrides with new keying
- Add defensive checks in D3D12CommandBuffer; update D3D12PipelineLibrary for new keying/state
- Move test shader to test.gsdef and update for new pipeline state syntax
- Remove obsolete files/interfaces and perform general code cleanups
- Update all usages and parsing logic for new pipeline state system

Ghost.Graphics/RHI/IPipelineLibrary.cs

@@ -22,5 +22,6 @@ public interface IPipelineLibrary : IDisposable
     /// <param name="filePath">File path. If null, load default library.</param>
     void InitializeLibrary(string? filePath);
     void SaveLibraryToDisk(string filePath);
+    bool HasPipeline(GraphicsPipelineKey key);
     Result<GraphicsPipelineKey> CompilePSO(ref readonly GraphicsPSODescriptor descriptor, ref readonly GraphicsCompiledResult compiled);
 }