fix: 压缩RDP实时画面传输

- 将原始RGBA位图压缩为PNG后通过WebSocket发送
- 降低低带宽代理链路下的RDP首帧延迟
- 增加位图压缩与异常数据测试

backend/controller/rdp_live_frame.go

@@ -0,0 +1,48 @@
+package controller
+
+import (
+	"bytes"
+	"encoding/base64"
+	"fmt"
+	"image"
+	"image/png"
+
+	rdpengine "ezops/pkg/rdp"
+
+	"github.com/gorilla/websocket"
+)
+
+// encodeRDPBitmapPNG 将实时 RGBA 脏矩形压缩为 PNG，避免原始整帧占满低带宽 WebSocket。 // Logan.Li
+func encodeRDPBitmapPNG(frame rdpengine.ServerFrame) (rdpengine.ServerFrame, error) {
+	if frame.Type != "bitmap" || len(frame.RGBA) == 0 {
+		return frame, nil
+	}
+	if frame.Width <= 0 || frame.Height <= 0 {
+		return rdpengine.ServerFrame{}, fmt.Errorf("RDP 位图尺寸无效: %dx%d", frame.Width, frame.Height)
+	}
+	required := frame.Width * frame.Height * 4
+	if len(frame.RGBA) < required {
+		return rdpengine.ServerFrame{}, fmt.Errorf("RDP 位图数据不足: got=%d want=%d", len(frame.RGBA), required)
+	}
+
+	img := image.NewRGBA(image.Rect(0, 0, frame.Width, frame.Height))
+	copy(img.Pix, frame.RGBA[:required])
+	var buf bytes.Buffer
+	encoder := png.Encoder{CompressionLevel: png.BestSpeed}
+	if err := encoder.Encode(&buf, img); err != nil {
+		return rdpengine.ServerFrame{}, fmt.Errorf("压缩 RDP 位图失败: %w", err)
+	}
+
+	frame.Image = "data:image/png;base64," + base64.StdEncoding.EncodeToString(buf.Bytes())
+	frame.RGBA = nil
+	return frame, nil
+}
+
+// writeCompressedRDPBitmap 发送浏览器已支持的 JSON PNG 帧，兼容现有前端绘制逻辑。 // Logan.Li
+func writeCompressedRDPBitmap(conn *websocket.Conn, frame rdpengine.ServerFrame) error {
+	encoded, err := encodeRDPBitmapPNG(frame)
+	if err != nil {
+		return err
+	}
+	return conn.WriteJSON(encoded)
+}