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/helper_windows.go

@@ -18,7 +18,7 @@ func RunHelper() int {
 	in := bufio.NewReader(os.Stdin)
 	out := bufio.NewWriter(os.Stdout)
 	for {
-		monitor, format, quality, err := readRequest(in)
+		monitor, format, quality, omitLayered, err := readRequest(in)
 		if err == io.EOF {
 			return 0
 		}
@@ -27,7 +27,7 @@ func RunHelper() int {
 			_ = out.Flush()
 			return 1
 		}
-		img, err := grab(monitor, format, quality)
+		img, err := grab(monitor, format, quality, omitLayered)
 		if err != nil {
 			if werr := writeErr(out, err.Error()); werr != nil {
 				return 1
@@ -46,11 +46,12 @@ func RunHelper() int {
 	}
 }
 
-func grab(monitor int, format string, quality int) (img models.CapturedImage, err error) {
+func grab(monitor int, format string, quality int, omitLayered bool) (img models.CapturedImage, err error) {
 	defer func() {
 		if r := recover(); r != nil {
 			err = fmt.Errorf("panic: %v", r)
 		}
 	}()
+	screenshot.SetOmitLayered(omitLayered)
 	return screenshot.CaptureMonitor(monitor, format, quality)
 }