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/config.py

@@ -129,7 +129,7 @@ class Config:
 
     script_fonts: dict[str, str] = field(default_factory=_get_platform_font_paths)
 
-    display: str = "terminal"
+    display: str = "pygame"
     websocket: bool = False
     websocket_port: int = 8765
 
@@ -237,7 +237,7 @@ GLITCH = "░▒▓█▌▐╌╍╎╏┃┆┇┊┋"
 KATA = "ﾊﾐﾋｰｳｼﾅﾓﾆｻﾜﾂｵﾘｱﾎﾃﾏｹﾒｴｶｷﾑﾕﾗｾﾈｽﾀﾇﾍ"
 
 # ─── WEBSOCKET ─────────────────────────────────────────────
-DISPLAY = _arg_value("--display", sys.argv) or "terminal"
+DISPLAY = _arg_value("--display", sys.argv) or "pygame"
 WEBSOCKET = "--websocket" in sys.argv
 WEBSOCKET_PORT = _arg_int("--websocket-port", 8765)