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/IResourceDatabase.cs

@@ -168,7 +168,7 @@ public interface IResourceDatabase : IDisposable
     /// </summary>
     /// <param name="id">The identifier of the shader to retrieve. Must refer to a valid shader.</param>
     /// <returns>A reference to the shader corresponding to the specified identifier.</returns>
-    Shader GetShaderReference(Identifier<Shader> id);
+    ref Shader GetShaderReference(Identifier<Shader> id);
 
     /// <summary>
     /// Releases the shader associated with the specified identifier, freeing any resources allocated to it.