feat(pipeline): improve new pipeline architecture

- Add TransformDataSource for filtering/mapping source items
- Add MetricsDataSource for rendering live pipeline metrics as ASCII art
- Fix display stage registration in StageRegistry
- Register sources with both class name and simple name aliases
- Fix DisplayStage.init() to pass reuse parameter
- Simplify create_default_pipeline to use DataSourceStage wrapper
- Set pygame as default display
- Remove old pipeline tasks from mise.toml
- Add tests for new pipeline architecture

engine/pipeline/registry.py

@@ -28,7 +28,7 @@ class StageRegistry:
             cls._categories[category] = {}
 
         # Use class name as key
-        key = stage_class.__name__
+        key = getattr(stage_class, "__name__", stage_class.__class__.__name__)
         cls._categories[category][key] = stage_class
 
     @classmethod
@@ -90,6 +90,10 @@ def discover_stages() -> None:
         StageRegistry.register("source", HeadlinesDataSource)
         StageRegistry.register("source", PoetryDataSource)
         StageRegistry.register("source", PipelineDataSource)
+
+        StageRegistry._categories["source"]["headlines"] = HeadlinesDataSource
+        StageRegistry._categories["source"]["poetry"] = PoetryDataSource
+        StageRegistry._categories["source"]["pipeline"] = PipelineDataSource
     except ImportError:
         pass
 
@@ -98,14 +102,48 @@ def discover_stages() -> None:
     except ImportError:
         pass
 
-    try:
-        from engine.display import Display  # noqa: F401
-    except ImportError:
-        pass
+    # Register display stages
+    _register_display_stages()
 
     StageRegistry._discovered = True
 
 
+def _register_display_stages() -> None:
+    """Register display backends as stages."""
+    try:
+        from engine.display import DisplayRegistry
+    except ImportError:
+        return
+
+    DisplayRegistry.initialize()
+
+    for backend_name in DisplayRegistry.list_backends():
+        factory = _DisplayStageFactory(backend_name)
+        StageRegistry._categories.setdefault("display", {})[backend_name] = factory
+
+
+class _DisplayStageFactory:
+    """Factory that creates DisplayStage instances for a specific backend."""
+
+    def __init__(self, backend_name: str):
+        self._backend_name = backend_name
+
+    def __call__(self):
+        from engine.display import DisplayRegistry
+        from engine.pipeline.adapters import DisplayStage
+
+        display = DisplayRegistry.create(self._backend_name)
+        if display is None:
+            raise RuntimeError(
+                f"Failed to create display backend: {self._backend_name}"
+            )
+        return DisplayStage(display, name=self._backend_name)
+
+    @property
+    def __name__(self) -> str:
+        return self._backend_name.capitalize() + "Stage"
+
+
 # Convenience functions
 def register_source(stage_class: type[Stage]) -> None:
     """Register a source stage."""