Feature: Implement H.264 and AV1 hardware encoding for remote control

Remark: Need to update FFmpeg static libraries to take effort

client/CFFmpegH264Encoder.h

@@ -0,0 +1,62 @@
+#pragma once
+
+#include "VideoEncoderBase.h"
+#include "common/config.h"
+#include <string>
+#include <vector>
+
+// 合规守护：DISABLE_FFMPEG_FOR_TEST=1 时整类移出编译单元，避免 GPL 传染（与 c0a632a 对齐）
+#if defined(_WIN64) && !DISABLE_FFMPEG_FOR_TEST
+
+struct AVCodecContext;
+struct AVFrame;
+struct AVPacket;
+
+// FFmpeg 硬编 H.264 实现。
+// Step 1: 仅探测 h264_nvenc 单后端，足以验证 FFmpeg 静态库集成链路。
+// Step 2: 扩展 h264_qsv / h264_amf / h264_mf。
+//
+// 输入像素：BGRA (bpp=32) / RGB24 (bpp=24)，与 CX264Encoder 完全一致；
+// 内部转 NV12 喂给 FFmpeg encoder。
+class CFFmpegH264Encoder : public VideoEncoderBase
+{
+public:
+    CFFmpegH264Encoder();
+    ~CFFmpegH264Encoder() override;
+
+    bool open(const EncoderParams& params) override;
+    void close() override;
+
+    int encode(
+        uint8_t* rgb,
+        uint8_t  bpp,
+        uint32_t stride,
+        uint32_t width,
+        uint32_t height,
+        uint8_t** lppData,
+        uint32_t* lpSize,
+        int direction = 1
+    ) override;
+
+    void forceIDR() override { m_forceIDR = true; }
+    void setBitrate(int kbps) override;
+    VideoCodec codec() const override { return VideoCodec::H264; }
+    const char* backendName() const override { return m_backend.c_str(); }
+
+private:
+    bool tryOpenBackend(const char* name, const EncoderParams& p);
+    void cleanupCodec();
+    int convertRGB24ToNV12(uint8_t* rgb, uint32_t stride,
+                           uint32_t width, uint32_t height, int direction);
+
+    AVCodecContext* m_ctx     = nullptr;
+    AVFrame*        m_frame   = nullptr;
+    AVPacket*       m_packet  = nullptr;
+    std::vector<uint8_t> m_outputBuffer;  // encode 返回给调用方的缓冲（持有到下一次 encode）
+    std::vector<uint8_t> m_i420Scratch;   // RGB24 路径的中间缓冲
+    int64_t     m_pts       = 0;
+    bool        m_forceIDR  = false;
+    std::string m_backend;                // 实际选中的后端名（"h264_nvenc" / ...）
+};
+
+#endif // _WIN64 && !DISABLE_FFMPEG_FOR_TEST