feat: implement Fence synchronization for CPU-GPU frame sync

D3D12 Core:
- Add ID3D12Fence1 and fence_value to d3d12_command
- Add fence_event for CPU waiting
- Implement wait() in command_frame for frame sync
- Implement flush() to wait all frames complete
- Add fence_value tracking per frame
- Signal fence at end_frame with incremented value

TestRenderer:
- Call graphics::render() in run()

Documentation:
- Add changelog for Fence sync implementation
- Update D3D12 Wiki with Fence sync section

docs/wiki/D3D12学习Wiki.md

@@ -211,6 +211,33 @@ _frame_index = (_frame_index + 1) % frame_buffer_count;
 
 环形缓冲区管理帧资源，确保 CPU 不会超前 GPU 超过 3 帧。
 
+### 6.4 Fence 同步机制
+
+项目实现了 Fence（围栏）同步，确保 CPU-GPU 帧同步：
+
+```cpp
+struct command_frame
+{
+    ID3D12CommandAllocator* cmd_allocator{ nullptr };
+    u64 fence_value{ 0 };  // 该帧的围栏值
+
+    void wait(HANDLE fence_event, ID3D12Fence1* fence);
+};
+```
+
+**同步流程**：
+1. `begin_frame()` - 检查 GPU 是否完成当前帧，未完成则等待
+2. `end_frame()` - 递增围栏值，向 GPU 发送信号
+
+```cpp
+// 帧结束信号
+++_fence_value;
+_cmd_frames[_frame_index].fence_value = _fence_value;
+_cmd_queue->Signal(_fence, _fence_value);
+```
+
+**围栏值溢出**：64位无符号整数，每秒1000帧需要5.8亿年才回绕，无需担心。
+
 ## 7. 渲染表面与窗口
 
 ### 7.1 render_surface 结构