D3D12: Implement ClearRenderTarget by tracking bound RTV handles

- Add m_boundRenderTargets and m_boundDepthStencil members to D3D12CommandList
- SetRenderTargetsHandle now saves bound RTV handles for later clear operations
- ClearRenderTargetView(ID3D12Resource*, ...) clears all bound render targets
- Reset() clears bound targets list
- Follows D3D12 best practice: RTV is bound via OMSetRenderTargets, then cleared

engine/src/RHI/D3D12/D3D12CommandList.cpp

@@ -65,6 +65,8 @@ void D3D12CommandList::Reset() {
     m_currentDescriptorHeap = nullptr;
     m_resourceStateMap.clear();
     m_trackedResources.clear();
+    m_boundRenderTargets.clear();
+    m_depthStencilBound = false;
 }
 
 void D3D12CommandList::Close() {
@@ -209,6 +211,18 @@ void D3D12CommandList::SetRenderTargetsInternal(uint32_t count, ID3D12Resource**
 
 void D3D12CommandList::SetRenderTargetsHandle(uint32_t count, const D3D12_CPU_DESCRIPTOR_HANDLE* renderTargetHandles, const D3D12_CPU_DESCRIPTOR_HANDLE* depthStencilHandle) {
     m_commandList->OMSetRenderTargets(count, renderTargetHandles, FALSE, depthStencilHandle);
+
+    m_boundRenderTargets.clear();
+    for (uint32_t i = 0; i < count; ++i) {
+        m_boundRenderTargets.push_back(renderTargetHandles[i]);
+    }
+
+    if (depthStencilHandle) {
+        m_boundDepthStencil = *depthStencilHandle;
+        m_depthStencilBound = true;
+    } else {
+        m_depthStencilBound = false;
+    }
 }
 
 void D3D12CommandList::SetVertexBuffer(uint32_t slot, void* buffer, uint64_t offset, uint32_t stride) {
@@ -324,6 +338,9 @@ void D3D12CommandList::DrawIndexedInstancedIndirectInternal(ID3D12Resource* argB
 }
 
 void D3D12CommandList::ClearRenderTargetView(ID3D12Resource* renderTarget, const float color[4], uint32_t rectCount, const D3D12_RECT* rects) {
+    for (const auto& rtvHandle : m_boundRenderTargets) {
+        m_commandList->ClearRenderTargetView(rtvHandle, color, rectCount, rects);
+    }
 }
 
 void D3D12CommandList::ClearRenderTargetView(D3D12_CPU_DESCRIPTOR_HANDLE renderTargetHandle, const float color[4], uint32_t rectCount, const D3D12_RECT* rects) {