fix(startup): make watchdog task keep agent alive

- Use Task Scheduler XML instead of /TR
- Run -ensure agent in-process, not child
- Add console close and panic protection
- Guard nil event channels after stop
- Add non-Windows stubs for startup/mutex

lib/clipmon/clipmon.go

@@ -98,8 +98,12 @@ func Stop() {
 
 func emit(event Event) {
 	event.Time = time.Now()
+	ch := events
+	if ch == nil {
+		return
+	}
 	select {
-	case events <- event:
+	case ch <- event:
 	default:
 		// ponytail: drop when full
 	}