Implement controlled app launch (T-401)

app-modern/platform/windows/platform.go

@@ -1,14 +1,28 @@
 package windows
 
+import (
+	"errors"
+
+	"softbox.local/core/application/launch"
+)
+
 // Edition identifies the application build channel shown by the UI.
 type Edition string
 
 const EditionModern Edition = "Modern"
 
+// ErrUnsupported reports that a Windows-only capability is unavailable on the
+// current host. Callers must treat it as an unknown state, never as a stopped
+// process or a compatible system.
+var ErrUnsupported = errors.New("windows platform capability is unsupported on this host")
+
 // Platform is the minimal boundary for target-specific capabilities.
 type Platform interface {
 	OS() string
 	Edition() Edition
+	IsCompatible(minOS string) (bool, error)
+	IsRunning(appID, entrypoint string) (bool, error)
+	Start(command launch.Command) (int, error)
 }
 
 // New returns the platform implementation selected by build tags.