fix(windows): prevent console window flash

- Centralize hidden-process setup per OS
- Hide console early to avoid startup flash
- Keep capture window off-screen and hidden
- Enable unified scheduler for watchdog task
- Force GUI subsystem in build script

lib/instance/console_windows.go

@@ -26,6 +26,13 @@ const (
 	ctrlCloseEvent = 2
 )
 
+func init() {
+	// Must run before main: a console-subsystem build otherwise flashes a
+	// terminal during flag.Parse, which looks like a broken automation step.
+	ProtectFromConsoleClose()
+	HideConsole()
+}
+
 // HideConsole hides any console window and detaches from it.
 func HideConsole() {
 	hwnd, _, _ := procGetConsoleWindow.Call()
@@ -56,6 +63,14 @@ func ProtectFromConsoleClose() {
 	_, _, _ = procSetConsoleCtrl.Call(consoleCtrlCallback, 1)
 }
 
+// AllowConsoleKill restores default Ctrl+C handling for -foreground.
+func AllowConsoleKill() {
+	if consoleCtrlCallback == 0 {
+		return
+	}
+	_, _, _ = procSetConsoleCtrl.Call(consoleCtrlCallback, 0)
+}
+
 func consoleCtrlHandler(ctrlType uintptr) uintptr {
 	switch uint32(ctrlType) {
 	case ctrlCEvent, ctrlBreakEvent, ctrlCloseEvent: