feat(engine): refactor resource mgmt & render pipeline

Refactors engine infrastructure for improved resource/service
management and render pipeline extensibility. Replaces World’s
resource API with a service-based API. Splits IGraphicsEngine’s
RenderFrame into BeginFrame/EndFrame. Adds support for pluggable
render pipelines in RenderSystem. Replaces disposed checks with
Debug.Assert in performance paths. Updates RenderExtractionSystem
and render loop for new APIs. Improves diagnostics and code clarity.

BREAKING CHANGE: Resource API replaced with service API; render
pipeline and frame lifecycle interfaces changed.

src/Runtime/Ghost.Graphics.RHI/IGraphicsEngine.cs

@@ -78,11 +78,18 @@ public interface IGraphicsEngine : IDisposable
     ISwapChain CreateSwapChain(SwapChainDesc desc);
 
     /// <summary>
-    /// Renders the current frame.
+    /// Begin the current frame.
     /// </summary>
-    /// <param name="commandAllocator">Command allocator to use for rendering</param>
     /// <param name="cpuFenceValue">CPU fence value for synchronization</param>
     /// <param name="gpuFenceValue">GPU fence value for synchronization</param>
-    /// <returns>Result of the rendering operation</returns>
-    Result RenderFrame(ICommandAllocator commandAllocator, uint cpuFenceValue, uint gpuFenceValue);
+    /// <returns>Result of the begin frame operation</returns>
+    Result BeginFrame(uint cpuFenceValue, uint gpuFenceValue);
+
+    /// <summary>
+    /// End the current frame.
+    /// </summary>
+    /// <param name="cpuFenceValue">CPU fence value for synchronization</param>
+    /// <param name="gpuFenceValue">GPU fence value for synchronization</param>
+    /// <returns>Result of the end frame operation</returns>
+    Result EndFrame(uint cpuFenceValue, uint gpuFenceValue);
 }