feat(adapters): Export MessageOverlayStage and MessageOverlayConfig

- Add MessageOverlayStage and MessageOverlayConfig to adapter exports
- Make message overlay stage available for pipeline construction

engine/pipeline/adapters/__init__.py

@@ -15,6 +15,7 @@ from .factory import (
     create_stage_from_font,
     create_stage_from_source,
 )
+from .message_overlay import MessageOverlayStage, MessageOverlayConfig
 from .transform import (
     CanvasStage,
     FontStage,
@@ -35,6 +36,8 @@ __all__ = [
     "FontStage",
     "ImageToTextStage",
     "CanvasStage",
+    "MessageOverlayStage",
+    "MessageOverlayConfig",
     # Factory functions
     "create_stage_from_display",
     "create_stage_from_effect",