feat: Sandbox implementation with seatbelt

sandbox/sandbox_windows.go

@@ -0,0 +1,13 @@
+//go:build windows
+// +build windows
+
+package sandbox
+
+import "errors"
+
+// newPlatformSandbox creates a platform-specific sandbox instance for Windows.
+// Currently not implemented - returns an error.
+// Future implementations will use AppContainer or Job Objects.
+func newPlatformSandbox() (Sandbox, error) {
+	return nil, errors.New("sandbox not yet implemented for Windows (coming soon: AppContainer or Job Objects)")
+}