feat(agent): add screen blackout feature

- Physical displays blanked via overlay
- Remote video and input keep working
- Exclude overlay from screen capture
- Add blackout API and UI toggle
- Wire flag through capture protocol

lib/capture/protocol.go

@@ -14,30 +14,38 @@ import (
 
 var ErrMonitorNotFound = errors.New("monitor not found")
 
-func writeRequest(w io.Writer, monitor int, format string, quality int) error {
-	_, err := fmt.Fprintf(w, "C %d %s %d\n", monitor, format, quality)
+func writeRequest(w io.Writer, monitor int, format string, quality int, omitLayered bool) error {
+	flag := 0
+	if omitLayered {
+		flag = 1
+	}
+	_, err := fmt.Fprintf(w, "C %d %s %d %d\n", monitor, format, quality, flag)
 	return err
 }
 
-func readRequest(r *bufio.Reader) (monitor int, format string, quality int, err error) {
+func readRequest(r *bufio.Reader) (monitor int, format string, quality int, omitLayered bool, err error) {
 	line, err := r.ReadString('\n')
 	if err != nil {
-		return 0, "", 0, err
+		return 0, "", 0, false, err
 	}
 	fields := strings.Fields(strings.TrimSpace(line))
-	if len(fields) != 4 || fields[0] != "C" {
-		return 0, "", 0, errors.New("bad capture request")
+	if len(fields) != 5 || fields[0] != "C" {
+		return 0, "", 0, false, errors.New("bad capture request")
 	}
 	monitor, err = strconv.Atoi(fields[1])
 	if err != nil {
-		return 0, "", 0, err
+		return 0, "", 0, false, err
 	}
 	format = fields[2]
 	quality, err = strconv.Atoi(fields[3])
 	if err != nil {
-		return 0, "", 0, err
+		return 0, "", 0, false, err
 	}
-	return monitor, format, quality, nil
+	flag, err := strconv.Atoi(fields[4])
+	if err != nil {
+		return 0, "", 0, false, err
+	}
+	return monitor, format, quality, flag != 0, nil
 }
 
 func writeFrame(w io.Writer, img models.CapturedImage) error {