Engine: 添加 /FS 标志修复 MSVC PDB 冲突问题

- 在 CMakeLists.txt 中为 MSVC 编译选项添加 /FS 标志
- 添加 OpenGL Screenshot 模块支持

engine/include/XCEngine/RHI/OpenGL/OpenGLScreenshot.h

@@ -0,0 +1,30 @@
+#pragma once
+
+#include <cstdint>
+#include <string>
+
+namespace XCEngine {
+namespace RHI {
+
+class OpenGLSwapChain;
+class OpenGLDevice;
+
+class OpenGLScreenshot {
+public:
+    static bool Capture(OpenGLDevice& device,
+                        OpenGLSwapChain& swapChain,
+                        const char* filename);
+    
+    static bool Capture(OpenGLDevice& device,
+                        OpenGLSwapChain& swapChain,
+                        const char* filename,
+                        int width,
+                        int height);
+
+private:
+    static bool SavePPM(const char* filename, 
+                        int width, int height);
+};
+
+} // namespace RHI
+} // namespace XCEngine