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/instance/console_stub.go

@@ -3,3 +3,7 @@
 package instance
 
 func HideConsole() {}
+
+func ShowConsole() {}
+
+func ProtectFromConsoleClose() {}